The sanctuary of Siena Cathedral is on the hill. Having gone down the stair you can get into the crypt of Siena Cathedral to have a look at beautiful frescoes of 13 century. The crypt is the underground spaces of a Roman church, which was on the site of today cathedral. For several centuries it was filled with sand used to reinforce the foundation of the cathedral. The crypt was opened for tourists only in 2004.
The cycle of frescoes (Nativity, Visitation, Deposition, etc.) covering the walls of the crypt was created in the period between 1270 and 1275. Through the example of these frescoes you can see the development of the Siena school of painting.
Due to moisture and sand the frescoes preserved their bright colours. It is unknown who painted the frescoes. However, it is suggested that Duccio worked at the frescoes although this Siena painter was very young at that time.