Cthonspace is an unusual sphere in that the interior is solid earth and stone, with a great number of large, planet-sized caverns and tunnels large enough for spelljamming ships to travel through. There sphere exists outside of the Known Spheres, and is inhabited by a variety of underdark races. The tunnels maintain gravity on all the surfaces, as well as atmospheres, although the larger tunnels are often airless voids in the center. Because of the large amount of rock in the sphere, all tunnels are full of loose floating asteroids of various sizes, few larger than a ship, though. Vast mushroom forests cover the walls of the tunnels; many species of which can be dried and used just as well as wood can outside the sphere. Other mushrooms glow slightly, giving the illusion of pale stars from a distance, along with softly glowing gems. Within the sphere exist three goblinoid ports which serve the same purpose as Bral, being somewhat cosmopolitan centers of trade and adventure.