The fascinating Buco della Serratura of the Priorato di Malta is an interesting place to visit in Rome. Through the portal's keyhole, the distant dome of St. Peter’s Basilica appears magically close in what is one of the city's most incredible sights. This place attracts hundreds of tourists ever day that want to see this, and as many other places in Rome you'll have to queue for some time to see it.

I visited it in June (high season in Rome), and the queue was quite long, but moves fast, as it doesn't take much time to see through the keyhole. Don't be discouraged if you really want to see it :) In the photos you can see how long the queue was for me and it took around 30 minutes of waiting (still a lot honestly), but for me it was worth it.