The Falkirk Wheel in Scotland is the world's only rotating boat lift. Completed in 2002, it was designed to reconnect the Forth and Clyde Canal with the Union Canal, which are separated by a height difference of 24 meters. Traditionally, this would require a flight of 11 locks and take an entire day to navigate. The Wheel can lift boats between the canals in just four minutes. Despite its massive size, it is incredibly energy-efficient; it uses Archimedes' Principle of displacement to ensure the weight of the two gondolas is always balanced, regardless of how many boats are inside. Because they are perfectly balanced, it takes only 1.5 kilowatt-hours of energy to turn the wheel—about the same amount of energy needed to boil eight kettles of water.