Fjaðrárgljúfur is a magnificent and massive canyon, about 100 meters deep and about two kilometres long. The canyon has sheer walls, and is somewhat serpentine and narrow. The bedrock in Fjaðrárgljúfur is mostly palagonite from cold periods of the Ice Age and is thought to be about two million years old. The river Fjaðrá has its source in the mountain Geirlandshraun and falls off the heath edge in this stunning canyon until it makes it down into Skaftá river. Fjaðrá has changed a lot in the course of time. Today Fjaðrá is often rather low in water and therefore hikers can safely choose to walk inside the canyon. However, wading is necessary fairly often. Deep in the canyon there are waterfalls so one needs to walk the same way back. Most people choose to walk along a walking path up on the canyon's edge while simultaneously enjoying the view above the canyon.