Blue Lagoon, Iceland

Bathers wade through the milky blue water of the Blue Lagoon on Iceland's Reykjanes Peninsula, with the main visitor building behind them. The lagoon is filled with geothermal seawater from the neighboring Svartsengi power plant, its color comes from dissolved silica, and the bathing area averages 37 to 39°C (99 to 102°F). Volcanic eruptions nearby have closed it several times since 2023, so check its status before booking.