Apart from being an architecturally interesting place, this is where they used to quarantine people inflicted with the Black Death (the Plague) in the 14th century!!
Now it's a park with a restaurant/bar and a sanctuary away from the noisy traffic.
We had stopped inside the old cemetery walls for a rest after a previous foray into the duomo area and thought it was some kind of children's area. It has a great space within the walls for football etc but the central building also serves food and drink. We ate lunch outside. Very good filled bagels with wine and chocolate...