This dungeon was initially designed as a Christmas gift for Puzzle & Dragons players. It made its first appearance in the English version as "Easter Sunday Dungeon", and may re-open under a new name for future holidays. This is a limited-time dungeon that can only be cleared once for the duration of each event.
In this dungeon, you can randomly acquire one of the Snow Dome Dragons. Once evolved, they are good grind team leaders for newer players, and once you no longer need them, they can be fed for a massive amount of XP. (Be sure to raise them to MAX level first!)