And this guide rounds up four blissfully calm locations where you can reflect, relax, or – for the romantics out there – swoon over the scenery without so much as a crowded corner.

Magnificent view of St. Peter’s Dome in the Vatican can be seen through a keyhole from the headquarters of the Knights of Malta on Rome’s Aventine hill.

Peek through the entry-door keyhole to see the perfectly framed dome, taking in three sovereign states (the Order, Italy, and Vatican City) in one glance. Spot the Pope: You don’t need to be ...