Cosmogony is a mod taking place during GLaDOS activation in the Enrichment Center. You are some of the few survivors of the neurotoxin disaster and with some help, you try to find a way out of Aperture. The map pack features custom content, a story deeply immersed in the Portal and Half-Life universe and more.
How to install:
1. Make sure you have Portal 2 purchased and installed on steam
2. Extract the Cosmogony folder into your sourcemods folder, you may have to make the folder yourself (C:\Program Files (x86)\Steam\steamapps\sourcemods)
3. Restart the steam client
4. The mod should show up in your steam library