Blue Lagoon is a Geothermal Spa located in a lava field between Keflavik Internation Airport and Reykjavik in southwestern Iceland. The lagoon is a byproduct of the nearby geothermal power plant. Superheated water is vented from the ground near a lava flow and used to run turbines that generate electricity.

After going through the turbines, the hot water passes through a heat exchanger to provide heat for a municipal hot water heating system and is finally fed into the lagoon. The warm waters are rich in minerals and bathing in the Blue Lagoon is reputed to help many people suffering from skin diseases. The water temperature in the bathing and swimming area of the lagoon averages 40 °C (104 °F) and is enjoyable year round, even in freezing conditions.