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This is a planet with a diameter 4.5 times larger than our Earth, but its mass is smaller. On the surface there is almost no atmosphere, but under the surface it is all pitted caves, leaving many thousands of kilometers down and all the air and all life are here. This is truly a planet of caves. It is rumored that a thousand years ago a highly developed civilization flourished here, ancient caves still store many strange objects and mechanisms left by it. But now everything is different, something happened to those ancient forerunners and now this mysterious world is divided in two: upper and lower. In the upper live intelligent beings, perhaps, descendants of an ancient people, here well governing and well. But at the bottom everything is different, there are terrible creatures, bloodthirsty predators who do not know mercy, for whom nothing is more hateful than the inhabitants of the upper world! No inhabitant of the upper world will ever willingly descend to the lower world.