After teleporting to the fifteenth floor, the conqueror found themselves in the middle of a grand hall. But this hall had no doors and only had sealed walls on all sides. Then the clearing condition of this floor appeared in the mind.
To clear this floor, they needed to do a very simple thing, that just needed to survive endless hordes of enemies and at the same time had to search for a special key hidden somewhere in this hall.
After finding the key, they just needed to find one of the enemy types who could use that key to open a hidden door to clear this floor. They themselves could not open the door and if they mistakenly killed the enemy type who could get them out of here, then that needed to wait for an indeterminate amount of time for that type of enemy to appear again.
