The outside world (also called outside edges or external area) is a destination, outside of all known sectors. It can be accessed through activating the zero anchor with actuator which gives the passage tunnel its coordinates or by the exit to the outside world in the Desert Sector.
Once entering the outside world, there is no way back anymore. The only building there is the external laboratory. Reaching it will mean the end of the game and the player can choose between two different endings.