The water is about as cold as it looks, and nobody cares once they put their face in. Silfra is a fissure in the lava field at Þingvellir, between the North American and Eurasian plates, and the visibility is the reason people fly in from around the world. Arctic Adventures run this snorkel tour with a maximum of six guests per guide.

The water is a mix of groundwater and meltwater from Langjökull glacier that takes decades to filter through the lava. Arctic Adventures put normal visibility at 70 to 80 metres. You float face-down in a drysuit, and the current does most of the work.

What's included in the Silfra snorkelling tour

• Þingvellir National Park admission fee
• English-speaking certified divemaster
• Snorkelling gear: thermal undersuit, drysuit, boots, snorkel, fins and gloves
• Free underwater photos taken by your guide
• Hot chocolate and cookies afterwards

Transport from Reykjavík isn't included. Neither are a towel and a change of clothes, and you'll want both.

Meeting point and what to bring

Park at Þingvellir P5, then walk about 400 metres back along the road to a smaller car park full of snorkel and dive vans, where your guide will be waiting. Be there at least 15 minutes before your start time. The whole tour takes about 3 hours.

Under the drysuit, wear thermal base layers (wool, fleece or synthetic) and warm socks. Bring spare clothes and socks, a towel (your face, hair and hands will get wet), outdoor clothing for the weather, and your voucher.

Who can join

This is where people get caught out, so read it twice. You need to be able to swim, be comfortable in the water, and be able to understand and speak English. Every guest reads and signs a medical statement in the Snorkeling Handbook, and some conditions require a doctor's letter. The tour isn't suitable during pregnancy. Drysuits fit guests weighing 45 to 120 kg and 150 to 200 cm tall. Glasses won't fit under the mask, so bring contact lenses or your own prescription mask.

Pro tip: go through the handbook's medical statement before you leave home. If you need a doctor's letter, you won't get one in a car park at Þingvellir.