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Photo: Sailko, CC BY-SA 4.0 via Wikimedia Commons
The town's best site is this gate built of massive volcanic stones in the 4th century BC. It's part of the town walls that were 4 miles around, twice as big as it is now.
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Great pulpit and altar. Notice how the entrance is through the baptistry, you couldn't enter until you were baptized.
Volterra's city hall is probably the oldest in Tuscany, at nearly 800 years, and inspired the design for the Palazzo Vecchio in Florence. The lavishly painted city council chambers are open to the public when not being used for official meetings.
A small 3-room museum of church art. Well explained in English.
Built in 10 BC. and has great acoustics, plus a great view, but a just as good view can be found at the city wall promenade for free. The theater can be viewed for free from Via Lungo de Mere.
Museo Etrusco Guarnacc
One of the best places in Europe for Etruscan art, it is filled top to bottom with it, though there are few English explanations.
This is a 14th century palace filled with great paintings, the highlights are the Annunciation & the Deposition of the Cross.