Italy has many historic monuments, battlegrounds, and museums related to World War II. If you're interested in visiting a few of them, the book A Travel Guide to World War II Sites in Italy makes a good companion. Available both on Kindle or in paperback, the book has details about visiting many sites with visitor information for each including how to get there, hours, and what to see. The book also has maps and photos taken in Italy during the war.
One of the most popular sites to visit is the reconstructed Abbey of Montecassino, the site of a famous World War II battle. Perched on a mountaintop between Rome and Naples, the Abbey has great views and is very interesting to explore.

