Dimension Keeper:
Did you know that these catacombs and necropolises were originally sealed in another dimension by the seal of Shunaiman, along with the magic that obscured the chasm that Lilith created to entice Shilen?
When the seal was broken, these structures appeared in this dimension! As a result, the power that was the seal exploded, and its fragments were scattered throughout the area. Part of that power collided with the wall of dimension and created a tiny crack in it. Through this crevice, a pathway formed between purgatory and this world! This is what we call a dimension gap!
Time and space are practically unrecognizable there, so it's wise not to stay in any one place too long! One must have a dimension fragment in order to enter there. This fragment was created from the force released when the seal was shattered.