For a memorable history lesson, visit the crumbling remnants of Terme Taurine and picture how it must have looked in its prime.
You're spoiled for sightseeing choice when in Civitavecchia. Terme Taurine is a good place to begin here, but there are loads of other fine places to discover. Terme della Ficoncella, Santa Marinella Beach, and Aquafelix are close to the once-important structure and and will cap off your day nicely.