Rome is full of hidden gems.
Yep. That is the line. To look through a keyhole on the Aventine Hill.
The thing is, it is kind of worth it. It is worth the walk, because Aventino hill is one of the quietest and nicest neighborhoods in central Rome. You can pass by ruins, rose gardens, an orange grove. And once you are at the top, the views are incredible.
The keyhole in question is the most famous attraction in the Piazza dei Cavalieri di Malta. If you are willing to wait, and/or if you get lucky and there is no crowd, the trick is to shimmy up to the large but nondescript green doors and get your camera ready.
Find the brass keyhole and look through it. You’ll see a garden filled with arched hedges.
Perfectly framing St. Peter’s Basilica.
See? Perfectly outlined?
Ok, ok. I have SEEN this view many times, but I have never managed a decent photo so here is one via AngMoKio at Creative Commons:
The view is well planned. You are looking through the gates of the church of Santa Maria del Priorato. The church belongs to the Knights of Malta, a Catholic religious order.
You can easily walk to the keyhole from Circo Massimo or Testaccio. The most common route is up Via di Santa Sabina from the Circus Maximus side.