The Thermae Bath Spa ★★☆
Take the waters at the modern Bath spa
In 2006, Bath resurrected its 2,000-year-old spa traditions by opening a new spa complex, a glazz-and-Bath-stone cube complete with an open-air rooftop pool with views over neary Bath Abbey and the city (nice and steamy in cooler weather).
There's also the sinuous indoor Minerva Baths, natural thermal waters with a whirpool and lazy river; all the usual spa treatments (massages, aromatherapy, watsu, hot stones, facials, etc.); and a restaurant for light meals.
The new chapel-like Wellness Suite includes both a Roman-style and a Georgian-style steam room, an infrared sauna, an ice chamber, and a Celestial Relaxation Room that's a bit like a small planetarium with New Age music and heated recliners (even this claims Bath heritage, inspired by Bath-based astonromer William Herschel, who discovered Uranus).
The Cross Bath
All of that is in the main New Royal Bath building. There is also a small, Georgian-era historic pool called The Cross Bath, with its own facilities, charging £18 (£20 weekends) per perosn for a 90-minute session—it's mainly, though, booked by small groups for private sessions.