Deep in the forests of central France, an unusual architectural experiment is half-way to completion, as a team of masons replicates in painstaking detail the construction of an entire medieval castle. The Chateau de Guedelon was started in 1998, after local landowner Michel Guyot wondered whether it would be possible to build a castle from scratch, using only contemporary tools and materials. Today, the walls are rising gradually from the red Burgundy clay. The great hall is almost finished, with only part of the roof remaining, while the main tower edges past the 15m (50ft) mark. Builders use sandstone quarried...