Underworld

The underworld is a location spoken of in Sonic and the Black Knight. Not much is know about this place. Supposedly, it is a separate realm of its own where untold dark and corruptive powers resides. It is also the home and natural habitat of the Knights of the Underworld. Some people, such as King Arthur, Merlina the Wizard and possibly Merlin, are able to interact with the underworld, allowing them to harness the place's forces for their own needs.