Limbo is a plane torn off the tree of life during the early years of the universe. It is also the place where all monsters hit by the orb of imprisoning wind up, including yourself (if you select yourself, or if you're unlucky). Once inside, no power or item can teleport you to any other realm. You'll be set free only when all monsters imprisoned in Limbo are defeated. You'll then be returned to the forest or the village without the orb.
For more information, see the description for the orb of imprisoning.