Thera the famous " keyhole of rome"- its a keyhole" in a door through which the dome of St. Peter's in the Vatican, several miles away, can be seen. Its located in the Garden of "Consiglio di Malta" on the Aventin, near to Santa Sabina and S Alessio. Unfortunatable you cannot get into the garden where you would see it like this:
Picture from: http://www.roma-online.de/besichtigung-aventin.html#piazza-malta )
The dome of St. Peter's appeares , perfectly miniaturized, and perfectly framed by green hedge.
We had to look through a keyhole of another door in the beginning of the garden. Was really very difficult to make a pic, thats the best I could make ...it looks exactly like the picture above, but you cannot photograph it.