You've probably heard this already but go to see the Trevi fountain - it's just there in the streets, you don't need a ticket; and in fact, a walkabout of that

You've probably heard this already but go to see the Trevi fountain - it's just there in the streets, you don't need a ticket; and in fact, a walkabout of that whole area is beautiful. I also really enjoyed an afternoon walking around St Peter's Basilica in Vatican City - the museum is stuffed to the gills with ancient relics that the catholic church 'collected' from around the world, and the architecture of the building itself is awe inspiring.