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.
Jet-Li, j2bq20002000, geogamer720p, jesus_sanlopez, TheHunterCarl, Tyr, psychologyfanatic333, ๖ۣۜRorek, มาวิน game caster, TheD.VaThatCrapsInTheHood, Vladimir Lenin, Chris alick comand, Sabotinekes, Alien, AustinDA, jonysambel, cheatpredaor155, xander0616, animal de bellota, antedomazet32, kongkritsakorn, Wolverax_Poot Poot, vans83324, BOT Fish, gabrielucho1, dobbinskyle543, deadzone0769, muscledbull, ropedi1981, halucard66, SuperBirdy, sergio97_04, deivizzz.milasauskas, esatainformatica, yannick_harter, Ejegggggg, LasseIsSpecial, kevin.cartoon, yebraa966, Aleeria G, christian.hexum, stevier69, Mexican Fanta, blade555355, sondt51, johnguzman9696, Dayman, alvaro.cope, SuMthinDiFrnt, XDRmix +360 others
