If you go, plan for a short 15–30 minute visit to the church of St. Ignatius in Campus Martius to see Andrea Pozzo's mind-bending ceiling fresco and its painted "dome" illusion up close. Entry is generally free with donations appreciated, photography is allowed without flash, and the church is often quieter first thing in the morning or late afternoon before evening services. Dress respectfully for a place of worship, watch for a few steps at the entrance, and combine this stop with the nearby Pantheon or Piazza Navona to make the most of your walkable sightseeing route.