Volterra's fortress, sitting atop the hill, can be seen from far away. The old Rocca was built in 1342-3. The new Rocca was constructed in the 15th century and walls were built to connect it to the original fortress, making it an excellent defensive fortress. The fortress was built just outside the Etruscan walls surrounding the city. This photo was taken from the archeological park where there's a good view of the fortress.
The fortress is still intact and impenetrable and is used as a high-security prison. The prison is the site of a unique gourmet restaurant - once a month (on Fridays) vegetarian meals are prepared by chefs in the prison and served by prisoners in a candlelit dining room inside the prison. Diners must be checked out by security ahead of time and pass through security check points before getting into the restaurant. It's very popular so you'll need to book in advance, 055 234 2777 (Italy country code is 39).