On a budget, skip Hop-On Hop-Off Bus — the spend outweighs the payoff.
€28–35 (24h)
A divisive option run by a couple of operators — Big Bus (open-top double-deckers, 8-10 min frequency, audio guide) and City Sightseeing — looping the Colosseum, Vatican, and central sights. The honest fit: it earns its keep for mobility-limited travellers and first-day orientation, but for anyone able to walk, Rome's compact, traffic-choked centre is genuinely faster and more interesting on foot, and the onboard commentary is thin.