Inside the Volcano

The Only Magma Chamber You Can Enter

Thrihnukagigur is a dormant volcano in Iceland's Blue Mountains, roughly 30 km southeast of Reykjavik. It last erupted approximately 4,000 years ago. What makes it unique among all the volcanoes on Earth is that its magma chamber did not fill with cooled lava after the final eruption. Instead, the magma drained away through subterranean passages, leaving behind an enormous hollow cavity beneath the crater. In 1974, cave explorer Arni B. Stefansson discovered that this cavity was intact and accessible, though it took decades before it was opened to the public as a tour in 2012.

The chamber extends nearly 200 meters deep in total, with the visitor area at 120 meters below the surface. The interior is vast enough to hold the Statue of Liberty with room to spare, and the entrance opening measures just 4 by 4 meters, giving no hint of the scale that waits below.

The Descent

The tour begins with a 3 km hike from the Breidabliksskali base camp across a landscape of ancient lava fields and moss-covered rock. The walk takes about 45 to 50 minutes at a steady pace and offers wide views of the surrounding Blue Mountain range. At the crater, you are fitted with a helmet and harness before stepping onto an open-top cable lift platform. The lift lowers you slowly through the narrow entrance shaft and into the expanding cavern below. The six-minute descent is when the scale of the chamber first becomes apparent as the walls open up around you and the daylight above shrinks to a small circle.

Inside the Chamber

At the bottom, you step onto the chamber floor and spend roughly 30 minutes exploring with your guide. The walls display a striking palette of reds, oranges, yellows, blues, and greens, all created by mineral deposits left behind during the volcano's final eruption. Iron oxides produce the deep reds and oranges. Sulfur compounds account for the yellows. Copper minerals create patches of blue and green. The effect is layered and textured, resembling an enormous abstract painting wrapped around the interior walls.

Your guide explains the geological processes that formed the chamber and points out specific mineral formations and lava textures. The acoustics inside are unusually quiet, and the air temperature stays around 2 to 4 degrees Celsius year-round, so warm layers are recommended even in summer.

Back on the Surface

After the lift returns you to the surface, the group gathers at the base camp where complimentary traditional Icelandic lamb soup is served, along with a vegetarian option, coffee, tea, and hot chocolate. The hike back to the parking area follows the same route across the lava fields.

Practical Considerations

The total tour duration is 5 to 6 hours including the hike, descent, and soup break. If you drive to the Blafjoll meeting point yourself, expect roughly 4 hours from start to finish. The tour operates in small groups and conditions can change quickly in the mountains, so waterproof outer layers and sturdy hiking boots are essential. Rain gear is provided if needed. Booking in advance is strongly recommended, as departures are limited and the summer season sells out quickly.