In the outskirts of Bandar Karahc you may find a building resembling a bowl turned upside down. It's covered with rusty plates, like a quilt, and it got exactly one entrance in the form of a small hole in the side, big enough for an adult to enter.
Anyone entering will find themselves following a winding, dark tunnel, sloping downward. At the end of the tunnel is a vast shaft, conical and seemingly bottomless.
Every ten minutes, the void fills with sand from the bottom up. It takes around two minutes to completely fill the space, after which the sand slowly descends again into the darkness.
This strange building is in fact the left lung of an interstellar, humanoid machine race.
These robotic creatures travels through the empty space looking for things to do. Although immortal, old age and the occasional plunge into planets' oceans makes their joints rust, leading to the inevitable and complete dismantling of themselves.
When this happens, their body parts spread across the universe, still functional; an arm may go into orbit around a planet, the head ends up in a sun, while the beating heart with its strong pulses may attract thousands of winged creatures from the reddish deep space.
Bandar Karahc got a lung. There are worst parts to get.