Glacial caves of Kverkfjöll
This geothermal area is hard to reach, but spectacular. A warm-water river runs beneath the glacier tongue in a 30km-long tunnel. Embark on a one-day hike to marvel at the enormous blue-tinged ice blocks, the fumaroles and the bubbling mud pots that come together in an unreal landscape. Alternatively, there is a shorter itinerary but, whichever you choose, get a guide to accompany you.