Crystalis

Crystalis takes place in a post-apocalyptic world, one hundred years after a global thermonuclear war has reverted civilization to a primitive, medieval existence populated with fierce mutated creatures. Science and advanced technology have been abandoned, though the old ways of magic have survived. The survivors of the terrible destruction built a floating "Tower" to prevent any future cataclysms, as its occupants would have the power to govern the world due to the Tower's weapons systems. A man known as Emperor Draygon, however, has revived the forbidden ways of science and combined them with magic. With these skills, he controls the world's last remaining military power and seeks to conquer what's left of the planet by attempting to enter the Tower