A terrestrial planet covered in vast oceans and dotted with isolated islands, Castilon was located in the Tashtor sector’s Castilon system, within the Mid Rim, also falling in the region known as the Western Reaches, in grid square I-16 on the Standard Galactic Grid. The system had one star, and the planet itself was orbited by two moons. It had an atmosphere that was breathable to the various species that inhabited it, including humans.

Castilon was the homeworld of the Chelidae, a species of amphibian sentients who preferred to live above the water, and was also home to many non-sentient creatures, including both the avian speagulls[ and aquatic creatures such as the sharvo fish, snarlfish, and the massive rokkna. A number of smaller creatures lived in the oceans of the planet and were often the prey of the larger creatures, such as the speagulls. While most of the planet was covered in ocean, there were occasional inhabited structures above the surface