One of the four planets formed when the Sartan sundered the Earth into four elemental realms in The Death Gate Cycle books by Margaret Weis and Tracy Hickman.
Pryan is the realm of fire, and is roughly like a Dyson Sphere in composition. There are four suns that never stop shining in the middle of Pryan, and all life exists on the inside of the planet. Because of the constant sunlight, plant life grows to humungous proportions, and it has taken over the surface. Moss beds on the tops of the vegetation provide a base for lakes and oceans.
Elves and humans both live on the surface of the immense vegetation. The elves prefer the actual treetops, while the humans prefer to make their homes on the moss plains. The majority of humans on Pryan are engaged in a civil war that is taking place between five kingdoms. The elves, rather than get involved, have chosen to capitalize on the war by acting as arms dealers to the humans. The magical weapons created by the elves are especially favored by the humans (who have no magic).
The dwarves on Pryan make their homes as far below the treetops as possible, favoring tunnels and caverns formed by the vegetation. They long for the earth and stone, and have little or no contact with the other two races. The look upon the other races with disgust and contempt.
On the portion of Pryan that is opposite of the wilds inhabited by the elves, dwarves and humans, there are giant fortresses called citadels. The Sartan lived in these cities (which had artificially created day and night) along with the lesser three races until they could no longer stand the bigotry and fighting between the different peoples. Eventually, the Sartan banished the other races from the citadels, and then abandoned them, disappearing. Outside of simply providing homes, the citadels had acted as communication towers, teleportation devices and beacons which focused the solar power from the four suns into the Death Gate conduits. The energy from the suns gave warmth and power to the people on Abarrach.
There are two other creatures on the planet, the good dragons and the Tytans. The good dragons live in the dense vegetation close to the ground. While the humans, elves and dwarves fear them, the dragons were actually created accidentally during the sundering as the ultimate manifestation of good (the Wave’s answer to the evil dragon snakes on Chelestra). The Tytans are giant, eyeless humanoids created by the Sartan as babysitters for the lesser races when they still lived in the citadels. When the Sartan disappeared, the Tytans, lacking instructions and locked out of the citadels, went on a rampage, destroying anyone who couldn’t answer their question: Where are the citadels?
Legend among the people of Pryan says that the three races used to live among the stars with the gods, but were banished because they were bad. What they call stars are actually the lights of the citadels, so there is truth behind the legend. It goes on to say that if the people live morally and honestly, they will eventually be called back to live among the stars.
Information taken from the novels themselves, and a summary at http://members.iquest.net/~jschatte/novels.html