The mountain Trölladyngja (Troll Mountain) is quite curious. This dwarf of a mountain (only 275 meters high) consists of palagonite like most mountains in the area. Trölladyngja and its surroundings is part of the Krísuvík Geothermal Area, but only recently so. Until 1975, there was no geothermal activity around the mountain, but a few years later things started to shift and change. Today Trölladyngja is geothermally very active. It is quite apparent in the colorful south side of the mountain and its surroundings.
Next to Trölladyngja is another mountain, Grænadyngja (Green Mountain) that is a bit higher (393 meters). The two mountains are commonly referred to as "The Sisters." Both mountains are geothermally very active, and also very popular amongst hikers. Both mountains are easy to mound, even for the inexperienced hiker. Indeed, one of the most popular and beautiful hiking routes in the Reykjanes Peninsula is the hike from Trölladyngja onto Grænadyngja, through the beautiful valley running between them.
"The Sisters" rise high above the lava field surrounding them, and are easily discernible from a long distance away, i.e. from the Capital area. Close by, you will find some of the most popular attractions in the Reykjanes Peninsula, such as the Blue Lagoon, the Bridge Between Two Continents, Reykjanesviti Lighthouse, Seltún and Gunnuhver.