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The second-greatest wall

The Great Wall of Gorgan

The Great Wall of Gorgan in Iran is 195km long, making it the second-longest wall in history behind the Great Wall of China. Built by the Sasanian Empire in the 5th or 6th Century to keep out (probably) the White Huns, medieval tradition also connects it with Alexander the Great and his legendary Caspian Gates.

Walking on water

Walking on water

Non-Newtonian fluids are usually liquid, but when force is applied they can change to be more solid or more liquid. Oobleck (a mixture of cornstarch and water) behaves like a liquid, but you can walk over it as if you were walking on water.