There were adventurers who found the dungeon before van, but since it were three groups who found it by chance and the guild rules are first come first serve (since the monsters had the chance to kill another and level up the first clear brings more exp and better loot) they are in the town and discussing which group goes first. the group who is allowed to go first had no problems until the undead floor, since van didn't clear it and left the golems he used to disarm the traps there, at which they need to call the others for help. when they reach the boss they need to request an even stronger adventurer group due to its rank and the troublesome abilities( energy drain if i remember correct) of the armor and weapon van enchanted, which break upon defeating the boss. and remember since van took everything this dungeon expedition is high cost no reward.