The Falkirk Wheel is a fascinating and beautiful piece of engineering.
Designed to replace a series of locks, boats float out along a viaduct from the top of a hill, then enter one of two “baths”, 180 degrees opposed on the twin arms of a wheel. The wheel then rotates 180 degrees, swapping the top and bottom bath. Out the boat moves, 35 metres below/above its start point.
P.S. I’ve had a few requests to show where this is, so I’ve included a map.