2300 years ago an eruption close to Mývatn formed Dimmuborgir. As lava flowed across the area, it passed over a lake, causing it to boil. This both quickened the cooling of the lava and caused pillars of steam to shatter parts of it. After it solidified, Dimmuborgir area became defined by large stacks of rock and many caves and caverns, caused by bubbles of intense steam.

This created a unique place, some believe that trolls live(or lived) there. When you walk around, it's easy to see why people believed that. Years later it was a location for Game of Thrones.