Thermae Bath Spa Rooftop Pool, England

Steam drifts off the open-air rooftop pool at Thermae Bath Spa, with the tower of Bath Abbey rising over the city behind it. The spa opened in 2006 in a building designed by Nicholas Grimshaw and uses Britain's only naturally warm mineral springs, which surface at about 45°C (113°F) and are cooled for bathing. Late afternoon and dusk are the times to be in this pool, and bathers must be 16 or older.