The main cultist temple. It's mythical guardian, skeletron, can only guard it during the day, so they also have skeletons, golems, and traps laid down by the mechanic. It is made of a dark blue stone called prismariene (made by smelting water dust, a powder obtained from water elementals) and is build in a Greek style, similar to Atlantis. In fact, it is believed that the infamous explorer J'oun Vmasez, credited with taking the only photo of Atlantis, actually took a photo of one of the entrenches to the dungeon, which explains it's derelict state in the photo.