While Alpine lakes and rivers enchant visitors with their aesthetic appeal, they’re often too cold for swimming. In 2017, however, Alpentherme Gastein opened in Salzburg, giving guests an alternative to normally chilly waters. At the thermal lakes, an innovative filter and cleaning system feeds hot water from the Hohe Tauren mountains into two bodies of water, which cover 1,421 and 404 square yards respectively. Bathers can sink into the warm waters and gaze up at the towering peaks before slipping onto the shore to cool down. Note: the lakes are only open from the beginning of May through October.