The Breach

The Breach is a rift in space and reality located in Arcadia. It was created by Aereth Shaw through use of a mysterious artifact, as well as the Arcadia Five unknowingly aiding him. Aereth and K'rrik both stepped through the Breach, entering into a lightless world of deep water. Although K'rrik quickly had to leave because he could not breathe underwater nor could even his powerful exoskeleton handle the intense pressure, Aereth seemed just fine through the use of a protective magic stemming from the rune magically inscribed onto his palm.
A moment later, a creature emerged from the Breach itself, a giant crab-like aberration with a fanged tentacle coming out of its back. Already hurt from their fight with the undead Ehlnofey and the Breach rapidly expanding and damaging the catacombs' structural integrity, the party was forced to flee upwards. Through a spiral staircase they eventually found their way into the Arcadian Citadel directly above them, though the expanding Breach was constantly on their tail as they made their escape. Not a moment after the party got out, the rift grew large enough to tear through and destroy most of the Arcadian Council's headquarters before finally ceasing to increase in size.
Little is known about the location on the other side of the Breach, but it's begun to be referred to as "the Fathom" by the common people.