Thermae Bath Spa

Bath's hot springs deliver more than a million litres of mineral water a day, and they are the only hot mineral springs in the United Kingdom. The rain that feeds them fell around 10,000 years ago, sank some two kilometres, was heated by the rock to an estimated 69 degrees and returns through three springs in the middle of the city - the Cross Spring, the Hetling Spring and the King's Spring, which supplies the Roman Baths. The water reaches the surface at about 45 degrees on average and is brought down to a bathing temperature of roughly 34. It carries more than 42 minerals and trace elements; the analysis published for the Hetling Spring gives 1,015 mg of sulphate, 358 mg of calcium, 340 mg of chloride, 195 mg of sodium and 193 mg of bicarbonate per litre, with 0.5 mg of iron. Boreholes sunk beneath the King's and Cross springs in 1983-85, at 68 and 32 metres, secured a clean supply, and a further Hetling bore was drilled in 1998 and 2011; the water is tested weekly and flow and temperature are monitored continuously.

From the 1970s the resource simply ran to the river Avon, and the modern spa dates from the completion of the restoration in 2006 after an unusually difficult build on a cramped site full of Grade I listed fabric and archaeology - the project went through planning three times and ended up a fifth larger than first designed. Thermal water now feeds four baths: the Cross Bath, the Hot Bath, the Minerva Bath and the open-air rooftop pool. Visitors meet two of them in the New Royal Bath, the glass-and-stone main building, where the standard ticket is a two-hour Thermae Welcome session covering the rooftop pool, with its view over the city and the hills, and the Minerva Bath, the largest of the thermal baths, curved and colonnaded, with a whirlpool. The same session includes the Wellness Suite, a circuit of an infrared room, a celestial relaxation room, an ice chamber and two aroma steam rooms themed on Roman and Georgian bathing.

The Cross Bath is a separate Georgian building across the street with its own changing rooms, an oval open-air bath where the water cascades in from the spring beside a commissioned fountain; the Cross Spring is recognised as an official sacred site, and the bath holds at most ten people, which is why it is also let for exclusive hire in ninety-minute slots. The main spa runs from 09:00 to 21:30 with pools closing half an hour earlier, every day except Christmas Day, Boxing Day and New Year's Day. It is an adults' spa - the minimum age is 16 in the main building, 18 for treatments - and phones are locked in pouches on arrival.