I feel like playing with some friends on Garry's Mod and we don't want to build. We want kind of like an adventure map, such as GhostHunt2, but that one is out of the question because they don't meet the game requirements on it. They only have EP1.
If you'd like, recommend either map, or a mod for HL2 or a map for HL2 that's adventure style and quite fun.
Don't recommend Synergy HL2 Co-op, I don't want to play the HL2 campaign.
