There is something mysterious and intriguing about spiral staircases. Atlas Obscura looks at some of the most magnificent spiral staircases in the world, with lovely pictures and facts you might not know. For example, the staircase at the Vatican Museum, pictured here, is actually a double helix, with one staircase going up and the other coming down. Link -via Curious Expeditions
Once, for carrying sculptures and things inside and outside there weren't elevators or similar automatic stuffs, and they used donkeys. To avoid the possibility that two donkeys looks one to the other while carrying stuffs upstairs or downstairs they built that double helix: a donkey that goes up on a spiral cannot see a donkey coming down on the other.
How does that work?
Dont both of them go up and down?