What is "dimmuborgir"

Dimmuborgir (dimmu "dark", borgir "cities" or "forts", "castles"); pronounced ) is a large area of unusually shaped lava fields east of Mývatn in Iceland. The Dimmuborgir area is composed of various volcanic caves and rock formations, reminiscent of an ancient collapsed citadel (hence the name). The dramatic structures are one of Iceland's most popular natural tourist attractions.