This download looks like a map. You need to place it in your maps folder inside the Garry's Mod folder.
You should end up with a directory structure similar to below
Don't know where the Garry's Mod folder is or how to extract zip files? See more useful installation tips.
roma.ersain, markjonathansanchezmariano, Gargan, grace7911, mmarcosdani5, AMUNG_hoshang, loboluiz48, eze_gomez2010, masascuate666, daniljaromuv, daniljaromuv, Fabricio4k, alex_valenciana, Eye Of Cthulhu#SaveTf2, Mitossauro_2039, Mitossauro_2039, ToninhoAnderlaine, °ZVN - |c10| |h15| |n|°, Dream♫, 101 |^1 Surreal ^4Sounds, demirtas-sam, Lop, spawnigor, [UDS] Luna, kornilovairina.86, SantiPaquitos, xX_GuMMYGuTZZ_Xx, (YT) AY| AkuroNerd3001, erproduction.639, Unknown Nomad, com.antilles, sillonmarron97, Звезда на ножках, Kritos64, Fruits, Golopența21, BeaterRiffin, Finnguy12345, reconditewarmowl71, Zolaf, Lamiiku, alexeev5as4, Dovahkiin, GeTToDOg, KaiyoSama, JoaoGPvP1, drey dg, NeoTeXaS, eucalyptus, davidyolande +229 others
