Dungeon Friends Forever Vol. 6

How could it possibly have taken this long for Van and Ryuka to enjoy a beach episode together? It may have something to do with this series taking place within the depths of a dungeon. But logic be damned! The dungeon monsters have managed to convert an entire floor into the exact sort of seaside retreat that'll get the childhood friends' hearts racing. Only, there's more to this underground sea than meets the eye. What mystery lurks beneath its waves?