In the Nintendo DS version, one exclusive area exists called the Dimensional Vortex. The Dimensional Vortex is a dungeon with that can only be accessed after beating the game at least once. When you return to your saved game, three new Gates will have appeared in separate time periods (12,000 B.C., 1000 A.D., and 2300 A.D.).
Like other dungeons in the game, the Dimensional Vortex varies depending on which time period you're in when you pass through the gate. Each time period specifies the reward from completing the dungeon: a permanent upgrade to one of three characters: Marle (the past), Chrono (the present), or Lucca (the future).
After completing all three different versions of the dungeon, a final, new, boss encounter is unlocked (as well as a new ending).
Dungeon entrance
Passing through any of the three Gates will take you to this area. You'll have to fight (or sneak) your way through several random maps from the game's locations before moving on.
After completing this first part of the dungeon, you'll enter into a room with a save point. Two additional paths lie in the room, one that takes you out of the Dimensional Vortex, and one that leads to the Twilight Grotto. This final area depends on which gate you entered through, and will also determine which boss you fight and which character receives a permanent stat boost.