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.
ultima_sword, i_wost_mi_weiner, polosur109, combine_stalker1, mds, Rice, erdemlioyuncu07, Dr. Pino Morsa, GrayWerewolf90, banettetejode.yt.2.0, Harambe Uchiha, drake9306, matteogta261, 03kj20f03232, hal 9000, Trash Panda, I Hate Mary Sues, KRiSTiAN, kaike9329, AerusDark, ♛Lordchris♛, , misha tak o, yzengardiens, Jazzper, kaikejch, mimod17, leon.zhnecz, Anstiméo [ק๏๏tเร], Adamska, DelKic Gamdom.com DotaX2.com, guillermobergh94, Milo, extrasven, kaikejcd567, PAGAN, Deimos, Stait x3, ramosleonardo833, kaikejcd745, cosmicchristv, Døç†øЯ, ShaunDash, my.little.pony.and.dinosaur, viktor_n_hristov, zanofa88, SGC | Vicky (AFK), Loser, kaikejcd44, kaikejcd44 +514 others
