Snorkel at Silfra, a top site in Thingvellir National Park, and see where two tectonic plates drift apart by 2 cm (1 inch) each year. Enjoy 100m (300ft) visibility in clear glacial water while spotting rock formations and freshwater algae.

The water comes from Langjökull, Iceland’s second-largest glacier. It is filtered naturally for up to 100 years through volcanic lava fields, resulting in some of the cleanest water on Earth.

Wear a 7mm wetsuit to dive beneath the surface and stay warm while swimming in the cold water. A wetsuit keeps you warm by trapping a thin layer of water between your body and the suit, which your body heat warms up.