User blog comment:KyouSakagami/I'm lost/@comment-26996876-20160406181100/@comment-26996876-20160407084544

It's actually the place where the Sea Dragons, Lava Lizards and Lava Larvae would dwell, in the futur updates.

But for now, there are only two things there: the Lava Castle (yet to be finished) and the Entrance to the (unfinished) Active Lava Zone aka. Sea Emperor's Prison.