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.
deviasaalessio.ad, 3KEN, ·.:.·Vector·.:.·, Dead_Rex, fetish., The Whitest of White Men, V.I.R.U.S., erolwolf072, olmez.56865, Hoàng, Say!!! Hi, Zack, famelnw, kcmukabi, Nauser, Gamer Person, tai38720, krejwen95, mossesx, usman.edelkhanov43, G2 Rizzo, i.r.vanade345, МореИзБалтики, conly, rudolfhessss, L490 是水我的朋友, ewadan255, I AM SPY, [TW]阿藍BOED-弟拜哥, TommygunJ, TommygunJ, vladdengyd, vladdengyd, mimszix3, Noчnaя БАБОЧКА, pinojimenez07, Somoslosjo, Sam[TIA||RHC], LeHawaw62, Stefan, Murder Inc., rladmlgus00, ☠Midnightstorm☠, ☠Rocky☠, bedirhan_seren59, danielbravoone, jhgpace, Nep (ﾉ◕ヮ◕)ﾉ*:･ﾟ✧, NekoButler, SuaMãe +107 others
