A small door at the base of the bell tower on the north side of the Cathedral leads into the church of San Giovanni, also known as the “crypt”. The crypt houses the baptismal font designed by Rossellino, and a collection of dazzlingly illuminated pages from the graduals that Pius II donated to Pienza Cathedral.
The crypt also houses the remains of sculptural decoration from the medieval parish church of Santa Maria and a set of three Flemish tapestries with Stories from the Life of the Prophet Daniel and an episode from Roman history depicting Sophonisba and Masinissa. These were donated to the Cathedral by Bishop Francesco Maria Piccolomini at Christmastide in 1593. From the crypt, one can enter the so-called “Cathedral labyrinth”, a system of drainage tunnels dug beneath the chancel in the early 20th century to counter the landslip problems that have plagued the Cathedral since it was first built in the 15th century.