Just as it was mentioned in the book, the Deep Sea Palace did not have any monsters inside it. This place actually looked like a palace and was extremely beautiful. Expensive looking chandelier and lavish carpet decorated it and it truly looked like a palace where a royal would be living.
But Rein and his lovers were unable to enjoy this luxurious place at all because this place was filled with traps. And it was not well hidden one or two traps either. Every step they took had traps. It was impossible to move forward without triggering them.
The person who designed this place was definitely not right in the head. The amount of resources he wasted was insane. The dungeon master of this place definitely had some screws loose in its head.