Foro Romano

Look down on it first from the Campidoglio terrace behind Palazzo Senatorio — free, and the only place the whole plan makes sense as one thing rather than a field of stumps. Then go in and walk the Via Sacra end to end. The three tall columns are the temple of Castor and Pollux, the round one is where Vesta’s fire was kept, and the brick hall with the great vaults at the top is the basilica of Maxentius. Go early or late: there is no shade down there and the stone holds the heat.