Palazzo Doria Pamphilj

There is a painting in this palace that terrified the man it depicts. When Pope Innocent X saw Velazquez's portrait of him, completed in 1650, he reportedly said "troppo vero" — too true. It is considered one of the greatest portraits ever painted, and when you stand in front of it you understand why: Velazquez captured not just Innocent's face but his entire personality. The suspicion, the intelligence, the barely contained aggression — it all comes through. Francis Bacon was so obsessed with this painting that he created over forty variations of it without ever seeing the original in person.

The Doria Pamphilj family still owns this palace and still lives here. That is what makes this place extraordinary — it is not a state museum, it is someone's house that happens to contain works by Caravaggio, Titian, Raphael, and Bernini. The audio guide is narrated by Jonathan Doria Pamphilj, a member of the family, in a wonderfully dry English accent (his mother was English). He casually mentions "my ancestor" the way most people mention a neighbour.

The Gallery of Mirrors was designed to rival Versailles, and in some ways it succeeds — the room is smaller but more intimate, and the light from the windows reflecting off the mirrors and gilded surfaces creates an almost liquid quality. The private apartments, opened to the public in recent years, include a chapel, a ballroom with a ceiling fresco by a student of Raphael, and intimate rooms with velvet walls.

This is one of Rome's great under-visited treasures. While the Borghese Gallery requires advance booking and the Vatican Museums are a rugby scrum, this gallery sits right on Via del Corso — one of Rome's busiest shopping streets — and most people walk right past it. The entrance is an unremarkable doorway between shops. Inside is one of the finest private art collections in the world.