Cyrtho Malath is one of the few pieces of the Lands of Magic that is known to have survived. Witnesses in Lake Starfall claim to have seen it fall from the sky, landing just west of the lake itself. How it survived isn't known, but it's believed the Ysthar protected it somehow.
Taking a step back, there are 3 races that were created by Malath: the Taldorians, the Ysthar, and the Akhevans. The Taldorians are pretty well known as a playable race. The Ysthar are rather secretive, primarily located in Cyrtho Malath trying to REDACTED which is explained as you progress through the wings of the zone. The Akhevans are much less known, even. The Mansion of Portals appears to have been of Akhevan origin, though, and some of the presences that roam there seem to be of Akhevan origin as well.
Short version: It's a Ysthar temple-ish place that fell from the sky.