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.
Bassarasun, litchi_wai, Mr.Freeman, bulldozer.ivanovich, Serge.Musoka, cachuli2016, CYBERGEN, •ENiM™, pedro.megaman.medeiros, ericnocevski, my.little.pony.and.dinosaur, zanofa88, THE TRAPPER, haikalmadjid, diegotomeldan31, ninja.sd, General Luck, davidbaumet1997, ButtSaggington, trifaniayu, [APC] G Froman, GaboSnow117, Naemy, joawnai, Bob, Bob, newkuro, comcom, J.Raul, hachin, Unit #952, Tyr, The_SAROKA (ง'̀-'́)ง, Прасковья, Alien, Carl., heiko.klopfer, Galacta-X, Galacta-X, Pleblo, FelipeColares357, Pitz Palu, ophiuchus, Hashtag_prettykitty, Ћира Ћирилица, M.granis, re15revisited, Beast, Animator ITA, akiramakasuren +83 others
