Spartakus and the sun beneath the sea

Long ago, the mystical civilization of Arkadia was one of the most advanced places on Earth, until the end of the world came and forced the land and it's people underground. After that great cataclysm, the Arkadians lived deep in the center of the Earth and created an artificial sun called the Shagma (Tiera in the American version). But one fateful day years later, the Shagma began to fade out. In a desperate act, the Children of this unusual civilization and their ship with a mind of it's own broke into to the secret museum, which was considered forbidden, except for the creatures who are in charge of it.