If the weather's taken a turn for the worse, why not head to Montemartini Museum? You'll be surprised just how many interesting facts you can discover about the past here.
When you've spent some time at this collection of historical artifacts in Aventine, why not make your way to St. Peters Basilica, Roman Forum and Piazza Navona? They're not too far from Montemartini Museum and also popular with many travelers.