Free icons in the historic centre
Trevi Fountain, Spanish Steps, Piazza Navona, Campo de' Fiori, Piazza del Popolo and the bridges over the Tiber are always free. The Pantheon is paid most days, so treat it as a low-cost stop rather than a free one unless you qualify for a free entry window.
Churches with museum-level art
St Peter's Basilica, San Luigi dei Francesi, Santa Maria del Popolo, Sant'Ignazio, Santa Maria sopra Minerva and San Pietro in Vincoli are the strongest free art stops. Cover shoulders and knees, keep voices low and check service times before entering.
Free views and cooling stops
Use the Pincio terrace, Gianicolo, Orange Garden and Capitoline viewpoints for photos without tickets. Refill at nasoni fountains instead of buying water near monuments; the public water is drinkable and cold.
Free Sundays: useful but crowded
State museums and archaeological sites open free on selected days, especially first Sundays. Arrive early, expect long queues and do not plan a tight schedule around them in high season.