Haven was a spherical size-A earth body, which meant that it was less than 5 miles (8 kilometers) in radius. It was the smallest of Glyth's satellites, a hollowed out asteroid that orbited between the first and second rings of its parent planet, 14,000 miles (23,000 kilometers) from the surface.
Gravity was spherical on Haven, as on most spherical worlds; however, it had an outside and an inside, more like a gravity plane. That is, one could stand on the outside surface of the moon, but inside the hollow rock, gravity was reversed, so that a standing person's head would point towards the core.
The interior was oxygenated, and many molds, fungi and mushrooms purified the air. The outside surface had no atmosphere.
While it appeared completely devoid of life from the outside, the tiny satellite was used as a neutral meeting ground for rival illithid factions. Spelljammers entered through a hole at the south pole of the rock. Only illithid ships were permitted to enter the moon. A ship that did not belong to an illithid—and thus did not have a very good reason to be there—was unlikely to ever leave again.
Haven was also the base for Glyth's security forces that patrolled the region around the planet for intruders. The mind flayers met there to trade, solve disputes, and plan their expansion.