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.
RandomSkillz99, Timmy_The_Turtle, Xhelron, Masuro, LetsFlyEm, Stifmeister, InsideFeeder, RoachPlay, Shadow, flee-511, DreamsofInsanity, TheKnightRider, _whitebird, George W Bush, van Gogh, LizJensen89, Tobinator, Momo_HP, Grundgütiger, Matze, Benjhof, Kevin D. Bob, Wilderhammer, Tosch, marcoschancabral, サーゼクス・ルシファ, LuziLp, Ewoksson, Rob The Bo$$, FettTorpedo, jan.c, mxx42, Benny, Itachi Uchiha, Rabbiton | Tobias, Lucy Redfield ♥ / (LucyUchiha), Cristino Ronaldo, BrainCat, Pudakasten, Venkun24, fairandsmooth, The KingKongHD, AirsoftMtz117, lamik.futsum123, FlammenwerferSS, Tbg.exe, janedano56, k1ngtzk3003, zTV, SilentCore +2472 others
