A hellish underworld, the whole universe is a massive cavern filled with inhospitable islands of blistering rocks dotting a roiling sea of magma. Literally, the floor is lava.
The denizens of this underworld appear to be communities of skeleton-like devilish monstrosities roughly 5 meters tall. Despite their frightening appearance, the denizens are actually very affable and help each other; they are all struggling together to survive, and they realize they’re all they’ve got.
Besides the sea of molten rock the denizens must worry about the magma centipedes. These can grow to 100 meters long, are eternally hungry, and can climb walls and swim through magma, where they are their most energized. It can take a whole army to defend a settlement from just one magma centipede, and while thankfully solitary they have been known to spit lava at attackers when hunting. Some denizens suspect they may also be somewhat intelligent.
Since the cavern-universe’s floor is a sea of magma, nearly all settlements are upside-down towers carved from massive stalactites on the cavern ceiling. They are defended from centipede attacks both by their vast distances from the sea below and with large if crude siege weapons to deter the approaching beasts.
(I do not own the images in the above collage, and all copyrights belong to their respective owners.)
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