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.
lertsri, jnccomeau, < blank >, Editor99, Editor99, jakubl0430, nossir_b, jqqq80, KeagasaurusRex, YARRAK, vitlisnik, ray545770, Ruben, Fabrolo, IVMofficial, demirhuseyin0725, El_Mignon59, remzicim, cartellowrider, Blackelaf2006, Joris Italiano | JL_Joris, gregoryaltuve05, rmep1978, WerPs, Aldres21, ismael.galouni, eexodiusv, RioSpain, Galaxy_Blizzard, Bubulek:P, pesker5, Kent McGregor, PantsuParty, pedroxelmejordetodos, martincitohuencho, E4jSS?!'^+//&;), [Nolipse]Mathis, ElManruel, richardishappy, gordontigo1971, nightmarenever78, WarTonas, TwgMlg, manzoej, manzoej, rare stickyfish, rare stickyfish, Tyson Latchford , MyGoldenMile, alfarob705 +771 others
