Also known as: Dungeon ni Deai wo Motomeru no wa Machigatteiru Darou ka OVA
Japanese title: ダンジョンに出会いを求めるのは間違っているだろうか OVA「ダンジョンに温泉を求めるのは 間違っているだろうか」
On their way back from the 18th floor, Hestia, Bell, and the others accidentally uncover a hidden, mystical hot spring, and they decide to stop by to refresh themselves until creatures lurking in the dark appear to attack them.