Land of Sagas and Eddas

Two to four degrees Celsius, all year. It is glacial meltwater filtered through lava for decades, which is why visibility runs to a hundred metres. You wear a dry suit over a thermal undersuit, so your body stays dry and warm. Your face, lips and hands are the parts that feel it, and after thirty to forty minutes in the water most people are ready to get out. Hot chocolate afterwards is standard.

No, but you must be comfortable in water. The dry suit floats you, so you drift along the fissure with a gentle current doing most of the work. You do need to be able to swim, and operators set minimum age, height and weight limits and ask about medical conditions on a form. Check the tour page for the current limits before booking. Glasses cannot be worn under the mask; contact lenses are fine.

Yes. The water is the same temperature in January as in July, and the visibility is the same. What changes is the air: getting into and out of the suit at minus five with wind is unpleasant, and daylight limits the departure times. Fewer people snorkel in winter, so the fissure is quieter. If you are here between November and February and want it, book the earliest slot for the best light.

Not on a standard dive tour. Operators require a dry suit certification or a logged number of dry-suit dives within the last two years, plus an open-water certificate. If you have neither, the two-day PADI dry suit course with a Silfra dive (/experience/19038/) gets you certified and in the fissure. Snorkelling (/experience/208/) has no certification requirement and shows you the same rock walls from the surface. Most people are happy with snorkelling.