Þríhnúkagígur is a dormant volcano in west Iceland, famous for its enormous magma chamber. It is the only magma chamber in the world that can be entered and has a depth of 213 meters (699 feet).
To enter it, you need to book the Inside the Volcano tour. There are also many other Lava Cave tours in Iceland.
Formation of Þríhnúkagígur
Þríhnúkagígur was once an active volcano in Iceland’s Blue Mountain range, also known as Bláfjöll. However, its last eruption, which took place nearly 2,000 years ago, led to an extraordinary and rare geological phenomenon.
Under normal circumstances, when a volcano erupts, the pressure release allows the magma chamber to either remain filled with lava, which cools and solidifies into rock or, if the chamber is fully emptied, the volcano collapses in on itself. This process creates either a hardened lava plug or a crater.
To the amazement of scientists, Þríhnúkagígur defied both of these expected outcomes. Instead of filling with hardened magma or collapsing, the chamber was mysteriously left completely hollow. It is believed that a deep underground rift drained the molten rock, leaving behind an enormous subterranean cavity spanning 3,270 square meters (35,200 square feet) with a depth of around 120 meters (394 feet).
To put its sheer scale into perspective, the entire Statue of Liberty could fit inside with room to spare, and Iceland’s iconic Hallgrímskirkja church could stand within it. Remarkably, despite the immense empty space left behind, the volcano did not collapse, and it has remained structurally intact for thousands of years—a geological rarity that continues to puzzle experts.
Discovery and Exploration of Þríhnúkagígur
Despite its vast size, the hidden magma chamber beneath Þríhnúkagígur remained undiscovered until 1974, when it was found by Icelandic cave explorer Árni B. Stefánsson. His discovery quickly made headlines worldwide, as scientists and volcanologists had never seen anything like it before. The formation challenged long-held theories about how volcanoes behave after an eruption, sparking intense scientific interest.
For decades, the volcano remained an inaccessible natural wonder, known only to a handful of researchers and adventurers. However, in 2012, Þríhnúkagígur was opened to the public for guided tours. A specially designed lift system, similar to those used in mining operations, was installed to safely lower visitors 120 meters (394 feet) into the heart of the chamber. This innovation made it possible for non-explorers to experience the breathtaking underground world that had remained hidden for millennia.
Þríhnúkagígur’s popularity as a tourist attraction stems from more than just its size and geological uniqueness. The inner walls of the chamber display a mesmerizing array of colors due to mineral deposits left behind by volcanic activity. Shades of deep red, burnt orange, vibrant yellow, emerald green, and even streaks of blue paint the rock walls, creating an almost otherworldly atmosphere. The combination of sheer scale, geological mystery, and vibrant natural art makes this one of the most extraordinary underground sites on Earth.
The Inside the Volcano Tour
The Inside the Volcano Tour is one of Iceland’s most unique adventure experiences, offering visitors the rare opportunity to step inside a dormant magma chamber. This is the only place in the world where people can descend into an intact volcano, making it a must-do activity for those seeking something truly extraordinary.
The tour begins with a scenic 3-kilometer (1.9-mile) hike through the rugged lava fields of Bláfjöll. The hike is mostly easy but slightly uphill and requires a reasonable level of fitness. Upon arrival at the base camp near the volcano, guests receive a safety briefing before being fitted with helmets and harnesses.
To descend into the heart of the volcano, visitors board an open cable lift, similar to those used in mining operations. The slow descent takes approximately six minutes, during which the sheer magnitude of the chamber becomes increasingly apparent. As the lift lowers into the depths of the volcano, the vibrant mineral-streaked walls come into view, creating a surreal and breathtaking sight.
Once inside, visitors have time to explore the cavernous space, marvel at the colorful rock formations, and absorb the eerie silence of the vast chamber. The experience is unlike any other, as standing inside an empty magma chamber offers a rare glimpse into the powerful forces that shape the Earth.
Tours to Þríhnúkagígur only operate during the summer months, typically from May to October, due to safety and accessibility concerns. The entire experience, including the hike, descent, and return journey, takes around 4–5 hours.
With its blend of adventure, science, and stunning natural beauty, the Inside the Volcano Tour is one of the most unforgettable experiences Iceland has to offer.
