Cattedrale di S. Secondiano
This beautiful cathedral, which practically abuts the Museo Nazionale Etrusco, is thought by many to be the among the oldest churches in Tuscany; parts of it date from the mid-6th century. It houses the remains of Santa Mustiola, the patron saint of the city. It has very little artificial light inside, so you can get a pretty good idea of how people experienced this space over the centuries.