Guédelon is somewhat of a crazy project: build a medieval castle from scratch using the same techniques as in the 13th century. It started in 1997 and is scheduled to go on until 2025.
The site can be visited and is in fact a live demo of medieval building techniques.
Here is a plan of the finished castle. It is typical of buildings made under king Philippe Auguste. While we visited, they were working on the chapel, which is now finished.