This may damage your saved game files! If you try this, it is recommended that you copy the game you try it on (although that does not ensure safety)
Go into any dungeon and find a ledge that you can jump off of that doesn't lead to a hole that'll lose you some life. Jump off of it and while in mid air, save and quit. Start a new game. When you get out of bed, you should fall through the floor and be under the world. From here, you can go basically anywhere, but it will lock up in some areas.
Submitted by: Thor