Peeping through any other keyhole is considered rude (and might lead to trouble), but there is one in Rome that substitutes sheepishness for awe, and guilt for beauty. Ill Buco di Roma is on one of the seven hills, a bit of a walk, at its best at dusk, but well worth it… Go ahead, don’t feel guilty, everyone peeks.
Piazza dei Cavalieri di Malta on the Aventine Hill… quite a sight. Swing by the Giardino degli Aranci while you’re up there, one of the great views of Rome, although be careful to not get locked inside (a story for another time!)
By the way, ever wonder what was on the other side?