This mod will allow you to begin in the Lambda Complex portal and work your way backwards to the start of the game. Some areas require a bit of out-of-the-box thinking in order to precede without using cheats.
Play Half-Life in reverse, stating with the Lambda Complex teleporter all the way back. Full version.
Play Half-Life in reverse, stating with the Lambda Complex teleporter all the way back. First fully playable version.
Play Half-Life in reverse, stating with the Lambda Complex teleporter all the way back. First fully playable version. * Added Hazard Course, because why...
This map pack is what I have made so far. Mostly playable. :)