Tip for traveling on the Rome metro (subway) system: instead of buying a ticket at the machine, you can just tap your contactless debit/credit/prepaid card at the turnstile. It's ticketless travel, so if an inspector stops you, show the card you used for payment. The ticket is valid for a total of 100 minutes on surface travel as well, starting from when you enter the subway (but valid for just one subway ride). Here's more info: https://www.atac.roma.it/en/tickets-and-passes/tap-go