Since there are already flesh and bone blocks it would be amazing to see either a boss you have to kill, which then turns into a dungeon (could be too large to implement). Or find a dead giant worm with its head on the surface of the planet, the rest of its body below the surface, it's mouth could be the entrance. Contra the game and Prey made me think of this idea.
Meat tunnel hey. *wink wink* Seriously though. That would be great. Maybe even an entity that covers the planet like in Unreal II. You would be walking around inside its belly etc
And since the devs want to include orbital stations later on why not... the corpse of a giant creature orbiting around a planet? Think about the dead gods in the astral plan of the D&D lore (cf: Neverwinter Nights 2: Mask of the Betrayer) or the dead Reaper in Mass Effect 2!
