Historian Ruth Goodman and archaeologists Peter Ginn and Tom Pinfold turn the clock back as they learn how to build a medieval castle using the tools, techniques and materials available in the 13th century.Ruth, Peter and Tom enter the surprisingly colourful world of medieval interior design.Peter and Tom render and limewash the inside walls of a guard tower, transforming its dark stone walls into a bright space.Ruth makes medieval paints which were used to decorate walls with ornate patterns. Most of the pigments are from ochre extracted from the earth - burning it creates darker tones. She decorates the castle bedchamber using designs based on those recently discovered at an 11th-century church nearby.Peter gets to grips with the castle's indoor toilets. An integral feature of medieval castles, the toilets were known as garde-robes, a French word for wardrobe. Clothes would often be kept inside them because it was believed the smell of ammonia from urine kept parasites at bay.Tom makes tiles - a process that begins with mining clay, before processing and shaping it. The tiles are then fired in a kiln. Four thousand tiles are fired at a time, requiring temperatures of over 1,000 degrees. It's a three-day process - and a tense one. If things don't go to plan, months of work will be wasted.It's estimated that over 80,000 tiles will be needed for the roofs and floors of Guedelon Castle.