Die Höhlenwelt Saga: Der Leuchtende Kristall (1994)

Starship pilot Eric "Speedy" MacDoughan traces his lost love, mysterious Maomi, to the barren planet 2S-126 in the Taurus 5 system, to discover that a network of caves leads to a gigantic cave world far beneath the crust - the Höhlenwelt ("cave world"). Down there, flying dragons and humanoid peoples live on a magical-medieval level under the despotic rule of an alien reptile race called Drakken. Eric meets the artificial being Cal (a deja vu for Hexuma players), who sends him to the cave world to retrieve a powerful energy crystal (the Leuchtende Kristall ("glowing crystal") from the game's title). And find Maomi, of course.