Station 51 is a single player mod for Half-Life 2: Episode 2. You are on the run from the Combine closing in on your outpost. Can you escape?
A detailed behind the scenes look at Station 51, and the lessons learned developing it.
Posted by SamCom on May 13th, 2013
I've put together a postmortem of sorts for Station 51. I always enjoy hearing why decisions were made in a level, so I decided to return the favor. This runs a little long (novelette length, in fact), taking the format of a walkthrough, detailing why I did what and other behind the scene tidbits. I finish out with the lessons learned and the next steps. If it's running a little long, at least skip to "Lessons Learned" near the bottom for the takeaway.
Mild gameplay spoilers, so you probably want to play through the mod before you read this. Let's begin!
Part 1: Rooftop
This first level started almost two years ago on paper, when I was sketching out ideas for the Rooftopville competition on PlanetPhillip. The only other single player project I'd released before was A Brief Detour in 2010. That project was a great learning experience, and helped me set goals for the first release of Station 51: fun combat spaces.
Combat in A Brief Detour consisted almost entirely of popping a few Combine troops directly in front of the player in a room with no room to maneuver, and no flanking opportunities. Also, the spaces were only loosely related- industrial to basement to apartment to industrial to Combine, all in the space of 20 minutes or less. So these problems were the focus.
I had a layout for the first rooftop section, all the way to the first Combine forcefield. I thought this was enough to get started, but it came back to bite me. All the other areas came after I'd blocked out the first rooftop area. They were sketched out individually, but the level as a whole wasn't on paper before I started. In retrospect, this was a mistake - once I'd blocked out the rooftop space, I hit a creative wall, and delayed and procrastinated for weeks because I didn't know what my next step would be. This is a lesson I still haven't completely learned, as we'll see later.
So the player starts asleep in a Rebel hideout of sorts, awakened by a radio warning from another station that the Combine are closing in. (That's me on the radio!) Right away, the player gets a view of where they're headed from the window next to the radio. There's an optional pistol in the crates, as a bonus for the exploration inclined player. As the player exits, a Combine helicopter flies past overhead, the player unnoticed for now. A little bit of foreshadowing there, since the player faces it down later. A short ladder trip up, and the player gets to see a Combine sniper directly above them get some practice in on some glass bottles. The player starts in a safe spot, so hopefully they're able to scan the area ahead and see a locked door and the grenade crate off to the left. They can make a break for the locked door and try and dodge the sniper, but that's an extremely risky proposition, if not impossible.
So after taking out the sniper with a well lobbed grenade, the player can move on to the padlocked door. A nearby dead Rebel wasn't so lucky with the sniper, but he did leave a trusty crowbar. There's also a goody crate visible but inaccessible just to the left behind a chain link fence - hinting that there's a way to the other side. The padlocked door assures that the player has at least some form of weapon before continuing.
Entering the locked door gets the player into a dark shack, with another locked door, this time with no padlock to shoot off. Since the room is dark, the vent up on the back wall should be pretty visible. A climb and some crowbar whacking, and the player's on their way, with another door, this one cracked open. Stepping towards it will trigger a flare from some Combine troops guarding the next section of roof. A shotgun is left in the player's path on their way up.
This is where the branching starts. Go left, and stay at roof level with easy access to more cover, or head up the stairs and get a better vantage point. The entire roof is open to the player from here.
Stepping out onto the roof triggers a Combine dropship, which drops troops at the far end of the roof in cover. Combine troops spawn on a balcony above the Combine dropship to help keep the player from spawn camping the troops piling out of the dropship. The gun built into the dropship helps with this as well.
A Combine shield wall is blocking player progress. Following a cable from the shield wall leads up to a combine console up in the attic of a nearby building. Maybe not the most realistic positioning - the only access to the attic is a roundabout route up stairs and a half-hidden ladder, but it does keep the player from just slamming a button and running through the space.
This entire chunk of roof serves as a combat arena. One approach is holing up in a corner and just waiting for the Combine to come to you. I tried to combat this by making sure there were multiple approaches and flanking paths for Combine to take, but this is still something players are able to manage. I still haven't found a perfect solution - the AI is built to counter this behavior by throwing grenades to flush the player out, but it doesn't work so well in indoor spaces.
Once the shield is down, the player moves into a warehouse building, with a pair of Combine slowing the player down. I added windows to this space to let an attentive player know what's coming and plan appropriately.
The next space is the train yard. The player starts above the space so they're able to get the lay of the land just before the helicopter from earlier appears. The drop down keeps the player from taking shelter in the building - they'll have to drop down to get the rocket launcher. I separated the rocket launcher and it's ammo to add some challenge to the encounter - getting rocket ammo will mean braving the top of the crates with little to no cover. It takes careful timing to grab the ammo without getting torn up.
I wish I could have made the rocket launcher a little more obvious - a few players complained about hunting for it. It is setting on a table in the open right under a crate of rockets, though. And the player has no where else to go, and they can't backtrack, so they're going to find the rocket launcher eventually.
The health of the helicopter is tweaked down severely - at default health it takes almost a dozen rockets to kill.I added some rappelling troops that drop in once the helicopter has been hit once, to keep the player on their toes. The shipping crates and high surrounding walls give enough cover that the resulting battle isn't punishing, it just takes carefully maneuvering and staying aware of the helicopter's position at all times.
After a volley of rockets, the helicopter is brought down, and a previously closed Combine door opens, with a red light and a few Combine to draw the player towards it. The player is now in another warehouse, this one with a combine base. A little quiet walk upstairs, and the player can see some rebels camped out in the middle of the warehouse. The player drops down (another sawtooth to keep the player from backtracking) and walks around to a Rebel waving and yelling for the player to come over.
Then, bam: two Hunters drop down through the skylights, and usually make pretty quick work of the Rebels unless the player is really fast on their feet. The warehouse floor is another combat arena - fairly large, with enough room for the Hunters to charge and for the player to dodge.
After bringing down the two Hunters, the player has a tiny breather, and then two more Hunters blast their way in through the loading doors. These were added since players complained about the battle being too easy if they used the rocket launcher from the earlier sequence. It also gets some more use out of the space, and lets the player exploit the knowledge of the space they gained in the first battle.
The player then enters a courtyard outside, with Combine soldiers appearing from the right. This used to be a straight path through to the air boat on the other side - the player can see the fenced off area they'll be arriving to in a bit. But I felt it was a little too short, so I added in the Zombie tunnels sequence, and use it as an opportunity to introduce the gravity gun.
The player enters the boarded up tunnel ahead, helpfully marked with a rebel lambda. Note the functioning flare pickup here, just for kicks. Inside the tunnel is a gravity gun, and it's last owner that seems to have met an unfortunate end. User error? There's also a zombie that's been sliced in half, the saw blade still in place. Pull out the sawblade, and the corpse drops down. A tiny touch, but I like it. There's also a Combine ball generator and shield wall, that was added in after the first release. This is here to make sure the player absolutely has the gravity gun before they continue, since they'll need it later in the second map.
Then: zombies! I tried to scatter physics props for the benefit of the zombies and the player: both can chuck physics objects at the other. I tried to mix in all different types of zombies - they simple type is just cannon fodder, the others keep the player on their toes.
The player clears out a wooden barricade, and gets jumped from behind by zombies hiding behind them. If the player's not careful, they'll run directly into the barnacles also placed here. But with some fancy footwork, the player can also lead the zombies into the barnacles. Barnacles are fun! Did you know barnacles will pick up grenades, hopper mines, even zombies? I didn't know until I made this map. This is one of the fun examples of emergent behavior built into Half-Life 2: simple rules like "The barnacle picks up all physics objects and NPCs smaller than a human" lead to pretty cool behaviors.
So a little more headcrab and zombie action, and a mercifully short vent section to get around a locked door, and the player is in a sort of laundry warehouse area. Not the strongest part of the map - I feel it's a little too tight to be a fun space, it needs more breathing room for both the NPCs and the player to have fun here. If I did it again, I'd expand this area or remove it altogether, maybe make it into a puzzle area.
The player then makes it to the airboat, parked in a shack. I really like this shack - it reminds me of the headcrab filled shack in the original Half-Life 2, a pretty atmospheric encounter. I'm also a big fan of the soundscape in the canal here, the chirping twilight bugs.The player jumps in the airboat. I made sure the player has the airboat when they leave with a jump that can only be traversed with the airboat.
I had bigger plans for the airboat, as I'll mention in the next section - but the player does get to end the level getting some air in a sweet jump. This is another space that could have used some more room to maneuver the airboat into position, but it works as is. This is where the original Station 51 ended, with a "To be continued."
On to the second map!
Part 2: Canals
I originally thought about adding a section in between the levels, with more dark tunnel and some puzzles, but it got scoped out. Also, the way forward with the airboat is blocked, and the player has to progress on foot. This wasn't always the case: it was originally planned to have the player drive the airboat all the way through the level, having to unlock gates along the way, with the final combine center being a canal gate control.
So why the change? Mainly because airboat levels require huge open spaces to be fun, and that's not really what I wanted to work on. Also, it becomes a royal pain to keep the player from leaving the boat behind when you don't want them to. Valve did this in Half-Life 2 with toxic sludge - the only way forward is using the boat, so you have to take it to progress. You also have to be careful to avoid sawtooth falls where the player can't get back to where they left the boat. So Valve did a pretty good job with it, but I didn't feel I had a whole lot new to bring to it. This is a personal project, after all, it has to be interesting to me too.
Original ideas also included a more sprawling level with optional encounter spaces - with the canal itself serving as a hub between the different gameplay areas. It's still an interesting idea worth exploring later - maybe having the optional encounters helping the player in some way, lowering the amount of resistance. But it felt like the player could just blow through all that content, so I decided to integrate the optional areas into the main flow. The brick building ruins and the concrete pillar ruins started as these optional side areas before being integrated into the main path.
This time, I did block out the entire level on paper before. However, that blockout changed dramatically from the paper version as I implemented it. Also, the original paper design didn't come to a satisfactory conclusion. When I ended up making major changes to the final Combine base, I didn't do enough planning on this portion, and ended up hitting another creative block once I reached it. Still, having a plan for the entire level was an improvement, and ended up resulting in a shorter development time.
The player enters the level in the airboat, dropping down into a mostly drained canal. I tried to keep some visual continuation of the last level. The shallow water adds some visual interest and softens the transition from water filled tunnels. Although the way forward is blocked, exploring the lower watery area will reward the player with some item crates. The brick ruins up the ramp started out as a very simple loop. It felt unnecessary and boring, so it was split into multiple rooms and a number of entrances to make it a more interesting encounter space, with room for Combine troops to flank the player.
The footbridge across the canal after the ruins has some metal plates that can be shot down by the Combine troops on the other bridge for a little physics fun. Breakable cover helps make the space feel more dynamic, and gives the player more reasons to move through a space. The player then gets an overview of the next combat arena before dropping down and fighting a whole squad of Combine troops. Hopefully the overview gives the player a chance to get a bearing on their surroundings and have at least ideas of what they want to do if attacked there. The dark tunnel with the force wall here used to be the main path, before the pillar ruins got repurposed.
The pillar ruins started as an optional goody area, before player feedback that it felt like a dead end. I think changing it to the main path was a good idea. Besides being more interesting to traverse, it also helped give the player enough height to get a good vista of their end goal, the Combine base.
I paid for this view performance wise - Source is not a big fan of these huge sight lines. I had never really attempted a space this big, so I didn't do as good of a job as I should have optimizing it, but some judicious use of hint brushes brought it back in line.
Below the ruins are some tantalizing supply crates - guarded by burrowed headcrabs that pop out when the player walk over and a trigger to spawn troops on the edge above the player. I like these optional encounters, and the player has plenty of cover to hide behind, and the headcrabs can end up distracting the Combine troops enough for the player to get an upper hand.
So the only way forward is to climb a ladder on the right side of the ruins, giving the player a nice view and a narrower than usual path across the beams. Tight enough to require concentration, but not so constricting that it's trial and error to navigate. A fall won't kill the player, and it might even give them another chance to trigger the headcrab event and collect some crates.
There's a small secret area - the left side drainage grate on the right as you're scaling the ruins can be entered, with a little hidey hole with a 357 and what looks like a damp if sheltered camp site.
While crossing the ruins, a single Combine soldier draws the player's attention to where they need to go and adds a little challenge to the crossing. The buried shipping container next to the lone Combine soldier contains supply crates - and two poison headcrabs hidden behind them. This is something Half-Life 2 likes to do - lure the player in with goodies, then spring a trap and make the player earn their reward. It feels fair, since the player had to decide to go towards the goods, they aren't being forced or railroaded.
The way directly towards the Combine base is blocked, but the player gets a preview of a later combat arena. This whole area is a swiss cheese of views into other areas. Not so great for performance, but it makes it feel more like a real space, and provides a preview of what lies ahead and helps the player set goals. This is partially inspired by the Fortress level from Uncharted (Youtube.com) - lots of previews of areas ahead, with grates letting the player preview areas and hint at the path to the goal.
Ascending the ramp leads to a fairly expansive combat area - with two Combine soldiers facing away from the player in the center, and a Combine scanner. These guys let the player know this is probably going to be a dangerous space, and let the player formulate a plan of attack. The player can even hang back and take them out from the ledge. Dropping down spawns two groups of soldiers - the first from the shielded tunnel entrance straight ahead, and a delayed spawn of more soldiers on the footbridge overhead.
The overhead troops are a little tricky - they encourage the player to move under the bridge, which has a grated bottom that lets the player shoot up and the enemies shoot down. This draws the player towards the next objective - a gate and a button. This is a very slow gate, keeping the player trapped for the next encounter. Soon after the player presses the button, combine troops rappel in on the far way near where the player entered, letting the player fight in a space that they now know fairly well, and approaching it from a completely different angle, getting more use out of the space. I like the battles in this area - lots of verticality, lots of different ways to approach it.
Soon after walking through the bridge, the player comes under fire from a rocket firing Combine tank perched up above some massive doors all the way at the opposite corner of the area, with some Combine troops sprinkled in the middle. The tank will try and fire where it thinks the player will be, but it can be faked out if the player is careful - so it adds a lot more risk to combat - the player has to keep jinxing to avoid the rockets while fighting the Combine troops. When the player gets close enough, it opens up with a machine gun instead.
The original idea for this space was a bit more complex: the tank would start out roughly where it was, fire at the player until it was damaged, then blow up a gate and drive through it, crashing on the other side. Cool in theory, but it was really easy for the player to break - they could just punt the tank with the gravity gun, and it would go flying and break the scripted sequence. I tried parenting non-puntable phys_boxes to the tank, no dice. So that was abandoned for a much simpler setup.
This tank fight space is filled with destructible cover in the form of wooden fences, which keeps the player from parking in one place and sniping at the tank. It gives the player momentary respite, but it doesn't last forever. More permanent cover is scattered around the edges of the area, in tank rocket range. There's a dead space in the cover right under the tank, but the player can't attack the tank from there. There's a box of rockets conveniently highlighted by a light, and perched up on a heap of trash so it's more visible. It's semi-protected with wooden fences, giving the player enough safety to grab rockets and duck back and forth to fire rockets at the tank.
The player already has a rocket launcher guaranteed, since they needed one to get past the helicopter in the first half. There's no other way forward through this space, and retracing the back is blocked by a sawtooth ramp, so destroying the tank is the next logical step. Destroying the tank blows out one of the metal doors and provides a way forward.
The next area is a little slower paced as a cooldown from the tank battle - it's full of hopper mines and supply crates, with a few barnacles thrown in. Fun fact - barnacles will pick up mines and blow themselves up. This is encouraged by having a mine directly in the player's path, with a barnacle just in front. This kind of surprised me the first time, so I tried to make it more likely to happen for players. You can also pick up triggered mines that jump for you with the gravity gun if you're quick enough. A little change of pace, with some supplies thrown in. I tried having some Combine troops appear above one the player was in the middle of the mine field. The idea was the player could lob mines at the enemies above, but it wasn't too fun, since there isn't a whole lot of space for the player or the Combine to maneuver.
The next bit gives the player another view of the Combine base, before making the player progress directly away from it. The wall shielding the drop makes sure the player has a chance to see the view of the base, and maybe explore the area off to the side up top with a few goody crates. I'm conflicted about turning the player away from their final objective - it's making the player move away from their goal, but looping back lets the player see the space before they enter it. If I had to do it again, I'd probably make this bit run perpendicular to how it is now, so the player isn't going backwards, while still allowing for the cross linked views across spaces.
Dropping down into the drainage area triggers a squad of Combine troops and a Hunter to enter from the far end. It's a pretty narrow space, but the covered walkways on either side provide options, and also let the Hunter sneak up behind the player if they're not careful. Kind of wish I could have used a pair of Hunters here, since they're designed to work together, but the space is a little too tight for that. The collapsed train bridge provides a nice little point of interest and hides a supply crate.
Entering the next half of the drainage area has Combine troops spawning above and dropping down, for more vertical combat. This area lets the player see the earlier combat areas from another angle, and they get the satisfaction of seeing how far they've progressed.
The next bit is a dark drainage tunnel. A bottle is triggered to drop from the ceiling near the entrance, so that perhaps the player is tempted to look up and see the supply crates up above, possibly perched there by enterprising rebels. More barnacles in the dark, with some convenient explosive barrels placed a little ways ahead. Past them, a pool of light and a large locked door, with a control room window looking over it. Hopefully the button inside is a big enough hint that the key to opening it lays that direction.
Time for some good old fashioned zombie shooting, but in the outdoors as opposed to the more usual dark and claustrophobic arenas. Lots of barrels and crates scattered about so the zombies get to show off their throwing abilities, and the player can choose to show off her gravity gun skills. Another hidden corner behind the generators with some tasteful graffiti, supply crates, and a poison headcrab. Advanced maneuver: the player can choose to run past the zombies here and use them as a distraction for the Combine troops ahead, if they saw them through the control room window. I always enjoy those AI vs AI battles, which we'll see more of in a bit.
Leaving the zombies behind, we enter a courtyard with Combine troops hanging out. Semi-protected routes around both sides of the arena, with the control room at the far end. Some looming Combine architecture at the other end, close enough to touch, letting the player know they're getting closer. Entering the control room lets the player open the door - but also triggers an alarm. Oops. Exiting the control room triggers a wave of Combine that use the side cover to flank the player, probably a surprise. Possible zombie stragglers might distract the Combine if the player ran past the zombies the first time - bonus.
So another arena where the player gets to fight back the way they came - a new perspective on the space, while letting them use their recently acquired knowledge of what works and what doesn't in the combat space, and maybe feel comfortable enough to take some risks and try new things. Also, I get twice as much use out of the hand crafted space. Everybody wins!
Entering the zombie area again, another small squad of Combine rolls in, letting the player fight a different enemy type in the same combat space.
The player gets back to the now open door, with a small quiet transition space, before ending up on a high balcony a few stories above a zombie filled room. Almost immediately after the player enters, a squad of Combine rolls into that mess, and the player gets to watch a sweet Combine vs. AI battle from relative safety above. Some grenades are scattered around a chair on the balcony where some bored Rebel whiled away some time. The player can choose to help who he wants, toss down some grenades and snipe from above or drop down into the melee. There are also some tempting crates that require a jump over a gap onto broken walkways - that collapse into the mess below when jumped on. Now I'm just messing with the player, and forcing them down into the space. I get some cheap laughs and maybe the player is surprised.
On exiting the ruined building, the Combine Base looms above the player - so close!
This Combine base went through a couple of revisions. It used to be a sort of gatehouse, when the player was still driving the airboat through. There was a passage below, blocked by a forcefield. The player would break into the Combine gatehouse, disable the force fields, and continue on their merry way in the airboat. This gatehouse was a more squat structure, with lots of windows. It was also symmetrical, which isn't very Combine. It also wasn't very imposing, didn't read very well from across the map as Combine, and didn't make for a very solid ending, just opening some gates. So it got scrapped and turned into what it is now. The area right in front sat empty for a long time - empty squares are hard to fill up,and I didn't want anything blocking the view of the Combine base.
The player fights their way up the stairs around the outside edge, makes their way to the top, and a gunship decides to drop in. Just below where the gunship shows up is a crate of rockets in the half destroyed gatehouse, with lots of crunchy windows and boards for the gunship to shoot up. So the gatehouse is the obvious goal in the space, but cover and individual rockets are scattered throughout the rest of the area, along with plenty of health and shield packs.
This area could possibly have been expanded, with more destructible cover forcing the player to move from place to place, but I feel guiding rockets past the gunship's defenses provides challenge enough, especially for such a late addition.
Once the gunship is shot down, a door on the warehouse flanking the base opens up. To draw the player's attention, a single Combine soldier walks out to see what all the commotion is, and a short siren plays from near the door.
Entering the warehouse, we get - shipping containers! Shipping container arenas brings back memories of the battles in Half-Life 1 and Opposing Force with the grunts, so it's partially a nostalgia choice, and also because it allows for easy off grid arenas.
An office of sorts serves as a goal and the only way over a wall of shipping containers. A quiet second floor, with supplies scattered about. The roof of the office gives the player a view of the Combine Base entrance, and a good vantage point for picking off troops guarding the entrance.
The entrance is spotlit by one massive light, with the entrance and a Combine ball generator highlighted to the side. The player needs to fight their way to the generator and knock the ball out to open the door.
As mentioned, I had to go back to the first map and make sure the player couldn't proceed without the gravity gun, so I added an earlier combine ball generator and shield wall right next to the gravity gun pickup that could open be bypassed with the gravity gun. Valve calls this a bullet lock - the only way past is with the item you'll need later. Back in the warehouse, a little unsubtle execution scene off to the side, just in case you weren't sure that the Combine were the bad guys.
So opening the door brings an assault team outside for a tough battle - the player will have to pull back to cover, and risks getting pinned over in the execution area and having to fight their way out.
Inside the base proper, the player gets to see where the gunship they fought came from in a gunship hangar, with an empty slot where the one they fought was. Kind of proud of my brushwork gunship support frame - inspired by the TIE fighter launch system and some concepts of scrapped gunship hangars from the Half-Life 2 concept book. The player has to circle around and across the top of the hangar, back into a very tall, dramatically lit room with tons of troops. Here the player gets the first hint of their true final goal - the teleport at the center of the base.
I'm not super happy about this final combat space - I feel it could use some more height differences, more spread out cover, and more staggered enemy spawns. This would be an area I would want to revisit, but it had already been through a ton of revisions - it was probably the least planned space when I started, and that ending up creating problems late in the game.
The battle leads to a passage wrapping around the outside of the Combine teleport room, with views into the inside and up to the goal, the control room. Inside the control room there's a Big Red Button, that triggers shaking, explosions, and arcing electricity, as well as blowing out the window and giving the player a route into the teleport room. I wish there was a better teleport effect to use, I feel the whirlpool is a little weak. And the teleport takes the player to an Arctic Combine Base? Shades of Half-Life 3? Maybe I was leaving myself open for a possible sequel. I always enjoyed the ending G-Man sequences where the player is teleported out to places unknown to await their fate.
And that's Station 51 in a nutshell. Or in a wall of text, anyway, but hopefully it gave some insight into the decisions I made and why I made them.
So what now?
So, as usual, huge room for improvement everywhere, and I can't wait to get started on a new project to incorporate the lessons learned. Only question is what's next, and I have no idea right now. I still haven't found a level editor or a set of tools and assets that I enjoy working with as much as I do with Source, but I want to explore my own ideas a little more, and make work that's accessible to more people than just those that already own Half-Life 2: Episode 2 and still have it installed after all these years. We'll see what happens!
Thanks for sticking through to the end!