Every afternoon at 5pm during the summer months, the diocese of Ascoli Piceno has a guided tour of six of its Romanesque churches, including the Battistero. The majority of these churches are not generally open to the public so it is a wonderful opportunity to see this style of architecture which was common in Europe from the 10th to mid-12th century.
The tours, which cost €4, are in Italian, although with a couple of days' notice, the diocese will find an English-speaking guide.
Outside of the summer months, a tour can be booked in English by calling the Diocese on 0736 252883 (if you speak Italian or me 0736 848664 if you don't!) a couple of days ahead.
The Battistero is always open from 10.00 to 13.30 and from 15.00 to 20.00.