The Aventine Keyhole
Also known as the Knights of Malta keyhole, the door of the Priory of the Knights of Malta on Aventine Hill until recently offered a perfectly framed view of one of Rome's most iconic landmarks.
The keyhole itself is predictably small (less than an inch in diameter), yet it affords one of the most unique perspectives of the city. In the past, anyone who stared through the keyhole was treated to a view of the massive dome of St. Peter's Basilica. It was a must-visit attraction.