Guédelon Castle in Treigny-Perreuse-Sainte-Colombe

You're standing at Guédelon, in a forest near the village of Treigny. Something unusual is happening here. A castle is being built. Not restored, but built from scratch, the way it would have been done in the thirteenth century. Have a look around. No cement mixers or tower cranes. Just stonemasons, carpenters and blacksmiths working with medieval tools. See those big wooden wheels? Those are treadmill cranes, the lifting machines of the Middle Ages. Someone walks inside, a bit like a hamster in a wheel, and one person can hoist 300 to 400 kilos.