Ramsus makes a good point. The map uses nearly all custom content, aside from 3 textures that come with all source games, so it can be played on nearly any game built on the Source Engine. If you're eager to try it but don't want to spend a penny, Team Fortress 2 is Free-2-Play and supports the map. The player start locations weren't meant for TF2 so if you do happen to go that route, just know you'll need to use cheats to fly out of the start area and into the actual fairgrounds.
