Graendalur is a green valley north of Hveragerdi in the Hengill region, where geothermal activity and lush vegetation meet. Hot ground, steam and other signs of geothermal activity occur in the valley and surrounding area. It is a popular outdoor destination, but geothermal habitats and vegetation are sensitive to trampling. Graendalur forms part of the wider Hengill geothermal system and provides a good example of how geothermal heat can influence water, soil and plant life. Visitors should use established walking routes.