Borgarvirki lies between Vesturhóp and Víðidalur, and at 177m above sea level it dominates the surrounding region. Made out of basalt strata, it has been used as a fortress for centuries. Borgarvirki is a natural phenomenon, altered by humans in earlier centuries. In 1949, the main entrance was renovated by workers. Borgarvirki is a volcanic plug (gosstapi), and the Icelandic sagas mention that in earlier centuries it was used for military purposes. Upon the fortress is a viewing dial.