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.
stuartcv123, Pioter ***********, naru38games, kruczek1234, dany, ❤️, Dobrodziej69, kachalko.matvei, avilesdiegoalejandro, rosas19774, alex_loner, VolkastFunny, fwater968, SS.GeStaPo, smartjuris, ricardobenjamin285, mikolajkwiatek411, Memelord06, bnjadeurr, artyomfevr123, trixfox223, Sientifico Mamadisimo, Henry Stickmin, Maurice the Horse, Itsyaboi Nick, MAN
