The Ultimate Parable is a mod in which you experience two entire smaller parables (stories) in order finally escape the first room you wake up in.
Now this, of course, is an April Fools release so it's not actually the real description :D
Installation:
1. Extract the .zip so you are left with a folder called "the_ultimate_parable" in which there are a number of other folders and a file called "gameinfo.txt"
2. Go to "{Your Steam installation path}/steamapps/sourcemods" and place the mod's folder inside.
3. Restart Steam and look for the sourcemod
Correct and Incorrect paths:
"{Your Steam installation path}/steamapps/sourcemods/the_ultimate_parable/the_ultimate_parable/{mod files}" -> WRONG
"{Your Steam installation path}/steamapps/sourcemods/the_ultimate_parable/{mod files}" -> RIGHT