Ouroboros

A schematic of the lost city of Ouroboros from Lego Ninjago
the build has only the main center of the city and there are no interiors
The Lost city of Ouroboros also known as the Ancient city of Ouroboros is a massive Serpentine city that was buried beneath the Sea of Sand after the Serpentine War. The Great Devourer was imprisoned underneath the city, and consequently, finding Ouroboros was a key element of Pythor and the Serpentine's plans for vengeance against the people of Ninjago. The city was originally used as the Serpentine's base before they set off to claim the Fang blades.

The city was built millennia ago and served as the place where the Serpentine studied the stars.At some point in time after Great Devourer's defeat, people of Ninjago sealed the snake under the Ouroboros.

After the Serpentine War, Ouroboros was abandoned and later buried in a large sandstorm and became the Lost City.