During my visit to the Cathedral of Siena, I learned that in 1339, a project began to expand the church, but the Black Death and some structural defects led to its suspension. The remains of the development are called the New Cathedral and include an unfinished facade, the Facciatone.
My climb up 131 steps (through one of those narrow spiral staircases that Italian towers are so famous for) of the Facciatione was rewarded by a panoramic view of Siena that includes both the Torre del Mangia (the Mangia Tower, which offers a great view, as well), the Duomo, and gorgeous tuscan rooftops.
(I went six years ago on a cloudy day and with a crappy camera. You'll probably be able to take a much better photo.)