Blue Lagoon is a geothermal spa in southwest Iceland, that is almost mid-way between Keflavik Airport and Reykjavík, close to the town of Grindavik. Entry starts at 6,990 kr per person (Aug 2019) and rises rapidly from there. This is a very popular tourist destination, attended by over 80% of tourists (around 1.3 million in 2017).

It is a byproduct of the nearby Svartsengi geothermal power plant. The warm waters are rich in minerals like silica and sulfur and bathing in the Blue Lagoon is reputed to help many people suffering from skin diseases such as psoriasis. The water temperature in the bathing and swimming area of the lagoon averages 37-39 °C (99-102 °F) and is enjoyable year round, even in freezing conditions.

- Wikivoyage