Isissia is a continent on the planet of Astro Prime, where the DSS trains young dinosaurs to become fully fledged astrosaurs. It is extremely cold and flat on the surface, which makes it a good place to practice astro-jet driving, but underground it is dominated by a labryinth of ice tunnels. It is the main setting for Terror Underground!, where Teggs and his friends are trapped in the tunnels with Colonel Erick the ammosaurus. They aren't alone, however, as a pair of vicious raptors named Sergeant Major Bonecrack and Pilot Komo have escaped from their prison of ice and plan to destroy the planet. However, the cadets and some giant spiders manage to stop the raptors.