I must recommend to anyone visiting Lake Bolsena a great guidebook called "Bolsena - Everything You Need to Know" by Fleur Kinson. My wife and I found this book REALLY useful when we visited Bolsena last summer. We found restaurants and even Roman ruins that we would never have found without it! It explained the whole history of the town, recommended walks and things to do, etc., etc. Excellent. There are extracts from the book to download on its website: www.bolsenaguidebook.com, including how to find Bolsena's hidden amphitheatre, some excursions to make from the town, and some cafe recommendations. Check it out!
I found a BRILLIANT book which covers every imaginable aspect of Bolsena and the lake - the only comprehensive guide in English I could find anywhere. It gave me all sorts of insider information, suggested walks, and really made me laugh, too! It was called Bolsena -Everything you need to know, and was by Fleur Kinson. I don't know if they sell it in bookshops outside of the Lake Bolsena area, but I got my copy on the internet and I saw it for sale in Bolsena shops. Ten out of ten!