From Muppet Wiki

Thra is the name of the world created by Jim Henson for the film The Dark Crystal. It is a planet with three suns: the Great Sun, the Rose Sun and the Dying Sun. The main landmark of the planet is the The Castle of the Crystal which houses the The Dark Crystal itself. When the movie starts, the shattering of the crystal has caused a dimming of the entire world.

To the southeast of the Castle of the Crystal lies the valley of the urRu, called the Valley of Stones, filled with mist, caves, and springs. Northeast are the Gelfling ruins, filled with stonework, tiled floors, and frescoes. Near to these is the Landstriders hill and the Podlings' village. Also in this area is a swamp which has animated vegetation and is filled with a crackling static charge shortly after dawn. To the far northeast is the Dome of Aughra.