You are able to revisit some of the dungeons after playing through them once, allowing you to collect items you forgot the first time or to get new ones.
When you replay a Dungeon, chests that have not yet been opened will still have their treasures. Additionally, golden chests are added to the dungeon that contain random loot, and respawn every replay.
When you replay a dungeon you're able to select the members of the group that will accompany you, but you won't be able to gain experience, altough you can keep the items and money the monsters drop. The monsters' levels will be matched with yours. The bosses you defeat in this mode will drop the same items they dropped the first time you beat them.
Replaying dungeons at different points in the game might change the enemy drops and chest contents. For example, if you replay the Haunted Mansion right after you complete Chapter 20 Haunted Mansion, the enemies drop about 5000-7000 gold and the random chest roulette will frequently land on cheap Enchanter swords. If you replay the Haunted Mansion during the Epilogue, enemies drop 8000-11000 gold and General Swords are added to the random chest roulette.