Brunnhorn is most often seen to the east of Vestrahorn, a much more well-known mountain located to the south of the town of Höfn. Like Vestrahorn, it is composed of a rock type called gabbro. Gabbro is known for its dark colouration and the fact it is pregnant with many minerals, most notably iron and magnesium; at Brunnhorn, deposits of gold and silver have also been discovered.

Brunnhorn has three distinctive peaks, which resembles the logo from Batman enough for the mountain to have earned its nickname. This unique shape makes the feature popular amongst photographers, particularly due to the fact it is surrounded by water in which, on still days, it reflects beautifully.

Brunnhorn is located on the Hvalnes Peninsula, which it shares with another gabbro mountain, Eystrahorn. It is part of a coastal area called Lón, a beautiful stretch with black sands and a wealth of wildlife, notably seals and migratory birds in summer.