For every meter of Rome you walk on the surface, there are 10 meters of city below your feet.
Plan this experience →Key underground sites: San Clemente Basilica (€10 — 3 layers: 12th-century church above 4th-century church above 1st-century Mithraic temple), Domus Romane di Palazzo Valentini (€12 — multimedia Roman houses under a palazzo), Catacombs of San Callisto (€8, Via Appia Antica), Bunker Mussolini (€15 guided tour). Organized tours: Walks of Italy Underground Rome (€69, 3.5h, covers San Clemente + Colosseum underground + Forum), Dark Rome Catacombs (€49, 3h). Colosseum underground: requires special ticket (€24 full experience, book at parcocolosseo.it — sells out weeks ahead). See where gladiators waited and animals were caged.