Rome's ticketed sites are the famous ones. Its free ones include some of the greatest paintings in Europe, and a trip built around them costs almost nothing in admission.
The Caravaggio churches
Free, open, and usually without a queue.
San Luigi dei Francesi — three Caravaggios in one chapel, the Saint Matthew cycle. Bring coins for the light box.
Santa Maria del Popolo — two more, the Conversion of Saint Paul and the Crucifixion of Saint Peter.
Sant'Agostino — the Madonna of Loreto.
Between them, more Caravaggio than most national galleries hold, at no charge.
The other free churches
San Clemente — three stacked levels: a twelfth-century church above a fourth-century one above a first-century Roman house with a Mithraic temple. The upper church is free; the lower levels take a small ticket and are worth it.
Santa Maria Maggiore — fifth-century mosaics.
San Pietro in Vincoli — Michelangelo's Moses.
Santa Maria in Trastevere — golden apse mosaics, and the piazza outside.
St Peter's Basilica — free, with a security queue that is long at midday and short at opening. The dome climb is separately ticketed.
Everything outdoors
The Pantheon's exterior and portico; the interior now takes a small ticket.
Piazza Navona, Campo de' Fiori, the Spanish Steps, the Trevi Fountain.
The Aventine keyhole — a door on the Aventine hill through whose keyhole St Peter's dome is framed by a garden avenue. Free, and there is usually a small queue of people who know.
The Orange Garden next to it, for the view.
Villa Borghese gardens — the park, as distinct from the ticketed gallery inside it.
The Jewish Ghetto and Trastevere, both for walking.
The water
Around 2,500 nasoni — cast-iron street fountains — run continuously with clean cold water from the aqueducts.
Block the spout with a finger and it jets upward from a hole on top. That is the design.
Carry a bottle. Buying water in Rome is unnecessary.
Cheap rather than free
Ostia Antica — a Roman port town nearly as complete as Pompeii, forty minutes on the metro and regional train, for a small ticket and a fraction of the visitors.
The Baths of Caracalla, vast and largely empty.
The Capitoline Museums, free for EU residents under 18 and modest otherwise, with the original Marcus Aurelius bronze.
Eating cheaply
Coffee standing at the bar: €1.20. Seated on a piazza: €4–6. Both prices are posted by law.
Pizza al taglio — by weight, from a counter — is a €4 lunch.
Eat away from the sights. Testaccio, Pigneto and San Lorenzo have the city's best cheap food and no tourist pricing.
Avoid any restaurant with photographs on the menu or a man outside inviting you in.