The Unending Dungeon

The  Unending Dungeon or Infinite Labyrinth is a hidden dungeon where Noir learned how to exist and invade with his Great Sage skills. The remarks of the four layers of Ghosts suggest that 200-300 years ago. It is Olivia, not Noir, who first went inside after it was sealed.

In addition to locating the entrance, you need to push the rotating wall on the left to reveal the stairs to a massive iron gate. No matter what kind of magic attack one summoned, it didn't seem like it'd budge in the least. It is also necessary to recite the required spell: "「The Hidden Dungeon only I can enter. Secretly becoming world strongest!」".

Known Floors
1. Floor: Golden Slimes full runner
 * 1) Floor

2. Floor: Several rooms with monsters and traps, one of which is Olivia, whose limbs are chained and crucified.

3. Floor: Open hallway with a Dead Reaper

4. Floor: Hall of the Dead with Ghosts

5. Floor: Various monsters:


 * Giant Jaw Ant
 * Giant Snake
 * Giant Frog
 * Tigerson

6. Floor: Army of Zombies

7. Floor: Maze of Corridors

8. Floor: Quiz to the 9th Floor

9. Floor: Forest full of animals and a weird tree nymph.

Trivia

 * This is the place where Noir meets Olivia.