Amphitheater
Tarragona, the Emperor Augustus's favorite winter resort, had arguably the finest amphitheater in Roman Iberia, built in the 2nd century AD for gladiatorial and other contests. The remains have a spectacular view of the sea. You're free to wander through the access tunnels and along the tiers of seats. In the center of the theater are the remains of two superimposed churches, the earlier of which was a Visigothic basilica built to mark the bloody martyrdom of St. Fructuós and his deacons in AD 259.