Minecraft wiki entry for Shelters, associated text: Dig a large series of tunnels underground (preferably clean, square-shaped, and free of obstructions or danger) and light it up to prevent mob spawns. The tunnel system can be built around a main tunnel or hub. Link the tunnel system with mines, caves, shelters, and landmarks that are frequented or owned by you or other players, providing an alternative to above-ground travel and quicker, easier access to mines and certain points of interest. Optional additions include beautification (such as different wall/floor materials or designs), minecart rails, boat canals, horse accessibility, displays (such as aquariums and dioramas), cave access points, designated mineshafts, simple shelters or work stations, and mob farms. This can technically also be built in singleplayer, in case you have multiple mines or places of interest across a wide area, but it serves more of a purpose in multiplayer.