This popular spa has been on the must-see list for Icelandic tourists for about 35 years. The man-made lagoon was founded when a pool of geothermal power plant runoff formed and locals began to notice the healing effects after bathing in it. The mix of sulfur and silica is said to have powerful effects on a variety of ailments, and thus, influenced the establishment of the Blue Lagoon spa that we know today. Plus, the milky blue water has become an identifiable feature in photographs, increasing its lure and appeal. And despite the crowds and high entrance prices, the Blue Lagoon remains a coveted experience - 80 per cent of tourists who go to Iceland visit it.