Ten years ago in the department of Yonne, in Burgundy, it was decided to build from scratch a 13th century fortified castle (un château fort) using techniques, tools and materials of the time. It isn't based on any remains, ruins or an existing building; it is an entirely new creation. They are expecting it to take 25 years in total.
Forty five artisans (quarrymen, stone masons, loggers, carpenters, tile makers, basket makers, rope makers, blacksmiths...) young people on work experience, volunteers, all are working together to increase our understanding of how castles were built. It is being built in the forest of Guédelon.
In the meantime, thousands of visitors are welcome to watch and observe the process from mid March until the beginning of November.
Fascinating, and I'd never heard about it before today. You can learn more at their own website.