Blue Lagoon, Iceland

The Blue Lagoon charges over $100 for entry and demands weeks of advance booking, yet its milky-blue water in photos contrasts sharply with a reality of crowded public pool conditions. Iceland’s tourism boom—from 300,000 visitors in 2009 to 2.3 million by 2023—was turbo-charged by Instagram. The country now hosts six tourists per resident, with the Blue Lagoon as ground zero. This is 30% more crowded than the typical geothermal spa rival, and its artificial setting is less natural than #10’s cenotes, despite a higher price tag.