The safest way to download is via the gm_fork Workshop page . Simply click the "Subscribe" button, and Steam will automatically download and install the files.
Download gm_fork: The Ultimate Guide to Garry’s Mod’s Most Atmospheric Map download gm_fork
Because gm_fork is so large, ensure your system meets the Garry’s Mod requirements . While GMod is generally low-end friendly, requiring only a 2GHz CPU and a DX9 capable GPU, maps of this scale benefit significantly from having the recommended and a modern processor to handle the AI pathing (nodegraphs) and complex physics. The safest way to download is via the gm_fork Workshop page