I know this is going to sound like a bit of a stretch, but having visited Pompeii earlier this year, the baths come very very close. I expected to see just the bath that you see in the photos, but it is so much more and spreads for some distance under the streets. Incredibly well preserved example of a Roman bath, almost as good as you will find in Pompeii, expect this one still has the geothermal water! The audio tour is excellent with a choice of recordings including children's version and commentary from Bill Bryson. Do not go to Bath and miss this
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