Secret Dungeon
From Elwiki
Requirements to unlock secret dungeons:
1. Must complete all maps for said town (1-3 stars), secret dungeon wont appear unless you do so. 2. To get inside secret dungeons, you require a pass. If in a party, all party members must each have one pass.
How to Obtain Secret Dungeon Passes
To obtain secret dungeon passes, you would need to finish a repeatable quest. (this quest appears after doing all the quests for said town)