Erandor

Erandor was one of the largest cities in the world, and was the capital of the Darksbane Empire. It was diverse, clean, and home of the Stewards of the house of Darksbane. Now, there is only the Sea of the Void. During the Shattering, N'aitar blew the city out of existence, so to speak. While it was not destroyed, it was released from the confines of this plane of existence. It drifts the ether, and once every several years or so, it will find a way to make brief contact with the real world. Those who are not careful can easily wander in and be caught. People caught inside do not age, and things do not decay, but time still moves. Some extremely lucky individuals can escape at future anchor points. Others simply drift with the city forever.
Where the city once was is a sort of tear in the fabric of reality - the Sea of the Void - a massive black pit. It has no bottom, no 'edges,' so to speak, the sea just ends. Various types of minor demons and the like have been known to come out of this rip, but they are typically kept back by the inhabitants of New Erandor.