An 【Age of the Gods Dungeon】. This one was made by the 【Demigod of Spring Water】 and it’s classified as a 【Demigod Rank】 dungeon.
It's placed in the Labyrinth City "Aquarium"
One of the dungeon's basic specifications is that it's made up of underground levels. In addition, many of its traps are water-based, and the monsters that appear there are primarily those of the elemental, fish, and shellfish systems.
The final layer is fifty floors down, and in the dungeon's long history, there's been very few stories of adventurers making it to that floor and successfully killing the boss.
Most of them aren't capable of defeating the boss enshrined on a specific level. Since this prevents them from delving deeper, it looks like these people enter the upper levels of the dungeon every day in order to collect items and earn daily cash income.