Thermal Pool, Austria
Bad Fischau, southern Lower Austria, 50km or so south of Vienna. This is a historic bath in our area (from about 1900). As you can guess it's natural spring water, there are even fish in the pools, but it's also not very warm. The 'thermal' water is only about 19°C, but as it is still a thermal spring some courageous people even go swimming there in winter.