Really nice town. The entrance into the back on the Duomo from the main square could be easily missed. It's on the stripy building next to the town hall. Go out the back (which is actually the front door) and have a look inside te baptistry.
It's not worth making the trip especially to see the Duomo alone but well worth popping in during a stroll around this lovely town.

The Duomo is a wonderful place to visit-a time to escape from the hectic 21st Century life-for a few minutes anyway. Make sure you are wearing the correct dress - there is a clear code of dress in the entrance.

Volterra is an medieval Etruscan hill town in Tuscany. We've never heard about it before our holiday. We went there by our hired car and really enjoyed this little town. Those before Roman time streets, old walls and gates, great views and unique alabaster shops make Volterra very special tourist attraction. Cathedral of Volterra is one of the places in a town we recommend to visit, you will like and remember it. Enjoy :)
http://www.volterra.net/

Go in expecting to see a great Duomo for a provincial little town and you won't be disappointed in the least. Don't go expecting to see something on par with Florence's Duomo - it's much smaller, less dramatic. But this one is beautiful nonetheless. For those (like me) who enjoy popping into the cathedrals and churches of Europe just to see architectural beauty in its purest form, it's worth it if you're in Volterra for the day.