You can get into Termini's ItaliaPass Lounge in one of two ways - either by purchasing a day pass for a one-time use, or by becoming an ItaliaPass member.
A day pass for the ItaliaPass Lounge costs $20, and entitles you to use the lounge from 9:00am until 6:00pm on that day. Learn more and purchase a day pass here.
An ItaliaPass grants you discounts on all sorts of things travelers need in Italy, such as airfare, hotels, rail travel, car rentals, tours, dining, and shopping. You can save up to $200, and membership is available to ItaliaRail customers at a special reduced price of only $49. Learn more and become an ItaliaPass member here.