A corrupt core dungeon. It's the same concept as a twin gate dungeon except the idea of dungeon cores. From what they've told me, a dungeon in this Elrev is opened when mana is poured into the dungeon's core, and closed when the core is destroyed. Meaning a dungeon can remain opened for an indefinite amount of time so long as they preserve the core even after raiding it, and can then be turned into what is known as an open guild managed dungeon as is the case with this trash dungeon that I have procured for the purpose of training my team.