Thrihnukagigur (Þríhnúkagígur) is a dormant volcano southeast of Reykjavík, famous for its huge, empty magma chamber. It is the only magma chamber in the world you can enter. It is 213 meters (699 feet) deep. Interestingly, no one went down into the chamber until 1974, and the find made headlines around the world – volcanologists had never seen anything like it before. Why?
Several thousand years ago, Thrihnukagigur was an ordinary volcano in the Bláfjöll (Blue Mountains) range. Sources give a fairly wide range for its last eruption – somewhere between 1,000 and 4,000 years ago – but we do know it had some very unusual consequences. Normally, after an eruption, a volcano’s magma chamber stays full of lava until the next eruption. If the chamber does empty, it is either “plugged” from above and surrounded by thick rock walls, or the crater simply collapses under its own weight. To the scientists’ surprise, neither happened at Thrihnukagigur. It is believed that a fissure beneath the chamber drained all the remaining lava, leaving a huge empty chamber behind.
The chamber is famous not only for its unusual origin but also for its amazing colors: mineral deposits paint the walls in vivid shades of red, yellow, green and blue.
Thrihnukagigur – tips and practical information
- The volcano has been open to visitors since 2012, but you can’t explore it on your own – only with a guide. Book your visit here: Inside the Volcano: hiking tour with pickup from Reykjavik (about 6 hours).
- Tours run from May 5 to October 30. With pickup from Reykjavik they take most of the day (about 6 hours, less than an hour of it inside the volcano), and they are quite expensive: 51,000 ISK (about $430) per adult and 25,000 ISK (about $210) for children aged 8–12, plus 4,500–6,399 ISK (about $40–55) for pickup from Reykjavik. Children under 8 can’t take part. [source: Inside the Volcano, checked September 11, 2026]
- Getting to Þríhnúkagígur takes some hiking: the parking lot is about 3.5 km (2.2 miles) from the crater, a 45- to 60-minute walk. You should be reasonably fit and ready for any weather. The operator provides all the necessary safety gear.
- You descend 120 meters (about 400 feet) into the magma chamber itself in an open cable lift, much like a mine elevator.
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How to get to Thrihnukagigur
You can drive to the tour’s meeting point yourself: from Reykjavik, take road 49 onto road 1 heading east, and after about 15 minutes turn right onto road 417 (Bláfjallavegur). The meeting point is the Breiðabliksskáli ski lodge in Bláfjöll, about half an hour’s drive from Reykjavik, with free parking. Without a booked tour, though, you’ll only see the surface and the entrance to the volcano, so there’s little point in going there on your own.
Tours with pickup start in Reykjavik, so driving yourself makes most sense if you have a rental car or are staying outside the city.
Unless you’re going from Keflavik, and aren’t IN Reykjavik…