One of the best things about taking the train in Italy – and, really, almost anywhere – is the opportunity to look at pretty scenery as you travel from one place to another. In some parts of Italy, however, there are scenic train routes that are specifically designed to be tourist attractions rather than simply modes of transportation.
Most scenic trains in Italy are operated by private companies, not Trenitalia, and they aren't intended to be transportation – in fact, most are basically circular routes, returning you to your starting point by either train or bus. Because these train trips are all about the view, cars with wrap-around windows are common.
Perhaps the most popular scenic train route in Italy is the Bernina Express, which connects Tirano in Italy to St. Moritz in the Swiss Alps. Along the way you'll see mountain peaks covered in snow, alpine lakes, and gorgeous valleys. Another beautiful route on the Italy-Switzerland border is through the Centovalli (“Hundred Valleys”), connecting Locarno and Domodossola. Both of these are included on Eurail passes, or you can purchase individual tickets.
There are also historic trains running on scenic routes in Italy, including some with steam engines and antique train cars. These, more than any other trains, do an excellent job of reminding us why we think of train travel as romantic to begin with.