The Nature Reserve Dimmuborgir, „The Dark Castles”, are among the most visited and admired spots on lake Myvatn.  It resembles a maze and people have to be careful not to loose their way, because prominent landmarks in the vicinity are not visible from the depression in the lava landscape.  It is rather a small area, only about 1 km in diameter.

About 2300 years ago a major eruption started, when a 12 km long volcanic fissure opened up a short distance away to the southeast.  During the eruption, the flowing lava met some kind of an obstruction in the Dimmuborgir area and a temporary lava lake was created.  Dimmuborgir are peculiar lava formations in the Younger Laxa Lava Field. A pool of molten lava, about 2 kilometres in diameter, was formed there during the fissure eruption of Ludentsborgir. This pool was drained when the lava exited towards Lake Myvatn, leaving behind high pillars of lava, which have taken on most bizarre forms. It is believed that these pillars were formed in the pool where steam percolated through the molten lava and cooled it. Horizontal lines, formed when the half-congealed lava crust of the pool gradually collapsed, are a frequent sight in the lava. The collapsing crust also coated the pillars with scoria, which can be seen in many places as a thin coating with vertical etchings.

Lava formations like Dimmuborgir have been found at the bottom of the ocean off the coast of Mexico but are not known to exist on dry land outside the Lake Myvatn region. The lava pillars at Hofdi (named Klasar and Stripar) are similar formations.

An earlier eruption, 3800 years ago, also altered the landscapes on the lake considerably. The eruptive fissures are side by side and the whole area offers great opportunities for short or long, light hikes.  Quite a few species of birds breed down there and the visitors are kindly asked not to disturb them during the breeding period and stay on the marked paths.  It is strictly forbidden to leave them and to climb the lava cliffs.
Painting David Haraldsson.