Sullust is the main planet of the system and homeworld to the Sullustan race. The planet is mostly rock and caves, as the cold environment does not permit vegetation to thrive. The atmosphere of Sullust is extremely toxic, as there are many volcanic regions that are very active, causing a near-constant outpouring of dangerous gases into the atmosphere. On average there is a volcanic eruption somewhere on Sullust at least once a week. The gases from the eruptions form noxious clouds that hover around the world, giving the planet an extremely dark and gloomy look from space.
Because of the dangerous conditions on the planet's surface, the majority of Sullust's organisms live in volcanic chambers underground. The Sullustans are extremely well adapted to their planet, building entire cities underground with thousands of kilometers of connecting tunnels leading from each and every direction. The Sullustans are highly advanced and their tunnel cities are considered some of the greatest architectural works in the galaxy. Hundreds of traders and galactic wanderers visit Sullust each month for the chance to walk around the grand chambers of the Sullust cave cities. At least one company has employed Sullustan architects to help plan and build future underground colonies. The largest collection of underground caves and tunnels on Sullust forms the capital city of Suubria. Thousands of inhabitants live within the main chamber of the city.
The caverns of Sullust provide adequate amounts of plant and animal life to feed the Sullustan people. Most of the animals are small, fast creatures that feed on the fungi growing underground. Some of the caverns are also used as farming areas, allowing large amounts of fungi to be cultivated. The hunting skills used in the caverns of Sullust has led the Sullustan species to have a naturally strong sense of direction.