The interior of this 13th-century church contains several engaging 14th-century fresco fragments and one real gem. Over the high altar is a justly lauded Crucifix, painted by Cimabue in the 1260s, then brilliantly restored and returned to this place of honor in early 2003. It's classic Cimabue, a work marking the start of the long transition from Byzantine triumphalism to Renaissance Humanism.

On the entrance wall are frescoes of the Crucifixion and the Life of St. Nicholas of Bari by Parri di Spinello. On the right wall, under a Gothic canopy, Luca di Tommé painted a very young Christ with the Doctors of the Church in the Sienese style. The chapel to the right of the high altar contains a 14th-century stone Madonna and Child and a delicate fresco of the Annunciation by Spinello Aretino. More faded frescoes line the church's left wall, and the last one on your right as you leave is a 15th-century St. Vincent Ferrer. According to Giorgio Vasari, this is the only known work by his grandfather, Lazzaro Vasari. Note that the church interior is very dark, but to the left and right of the altar are fuse boxes where you can switch on the lights.