The planet of Rythea contains the following regions:
In the middle of the Loric Ocean, there was once a large cluster of islands known as Lorica, which was surrounded by a thick perpetual fog. In 1490 DR, Lorica was swallowed by an Ether Cyclone (see page 49 of the Dungeon Master's Guide), which continues to rage to this day. Some characters and even entire regions from Lorica survived the disaster, turning up in the far reaches of the Material and Astral Planes. It is currently theorized that the Wayward Isle originated from the Lorican Ether Cyclone.
At about the same time that Lorica disappeared, the islands of Karmell vanished under the sea.