Basilica di Santa Maria Maggiore is one of Rome's major churches, and you should plan for a focused 20 to 45 minute visit to see its 5th century mosaics, lavish gilded ceiling and papal chapels. Entry to the church is free but there is usually a security check, and the museum and crypt often charge a small fee. Dress respectfully, cover shoulders and knees, and know that parts may close for services so arriving early helps you avoid crowds and closures. It sits a short walk from Termini and right by the Vittorio Emanuele metro stop, and photography is generally allowed provided you are quiet and respectful during worship.