Get Addon Gmod Map Expansion by Logic Switching: https://osgmod.com/gmod-scripts/3959/dynamic-map-switching-world-expansion

Video: https://www.youtube.com/watch?v=KOdTV15Gfeo

"Addon Gmod Map Expansion by Logic Switching" for Garry's Mod, allows different maps to be dynamically linked in the game. Players physically move to transition points, and when the required number of players is present, as determined by the server owner, the server map switches to the next map. The players then appear consistently in the new map. This mod allows players to trigger these map changes autonomously, which maintains the immersion of the game. It allows you to create a game world that spans several maps, and to design dungeons, high-risk zones and quests that take place on other maps. You can define transition conditions based on rank or job. This add-on gives players control over how the game world evolves as a function of their activity.