Seljavallalaug Swimming Pool in Iceland is the oldest pool in the country, built in 1923 to teach people how to swim. The 20-minute hike to the pool offers scenic views, but be prepared for the disgusting changing rooms filled with trash and mud. The water temperature is warm at best, not hot like a typical hot spring, and is filled with algae. Despite its free entry, visitors are encouraged to leave no trace and help maintain this hidden gem for future enjoyment.