Reykjadalur is an active geothermal area, filled with hot springs, mud pools and a hot river. To reach the Reykjadalur Thermal River you first have to walk 3,5 kilometers and it takes you around 45 to 60 minutes. You can park your car at Gjaldskylda parking (paid). The hiking trail is quite steep in some parts but it takes you through an impressive mountain landscape. And after the hike you can bathe yourself in the hot river and give your tired muscles a moment of rest. The temperature in the river varies and gets warmer the more you go upstream. Find yourself a spot with a temperature that suits you and enjoy the beautiful scenery. The way there is mainly uphill, meaning that the way back is mainly downhill. So even when you're back at your car, you'll still be able to enjoy your rested muscles a bit.