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.
re15revisited, BR0_crafter, jorgenieblas, OHikareO, EMROLEHEROS, YaLikeJazzz, Diggingwolf2605, Winter, DerpaFett, |cYp|^^xHSx^^, JustAkan, Arctic0ne, elpablo01nick, Keren1altman, The Controller's™, Soldier
