Reykjadalur means “steam valley” in Icelandic, and the trip here is a must for everyone who's visiting Iceland. Reykjadalur Hot Springs is just a 40 minute drive south of Reykjavik. They are located in the beautiful Reykjadalur valley, near the town of Hveragerði. The hot springs can be reached via a short 3.8-km (2.36-mi)trail that features amazing views. The trail head can be seen right near the Hot River cafe outside of Hveragerði. It takes about an hour of walking to get to the steaming hot river flowing through the valley. In about 15 minutes you will also see several geothermal water holes.
At the end of the hike, there is a specially designated swimming area with wooden docks and a few changing stalls. The farther you get upstream, the hotter the water is, so it's easy to find a spot with a temperature just right for you. Since the trail can get crowded, it's better to start your hike as early as possible.
The Reykjadalur is part of the Mt. Hengill area, an extinct volcano, which was active 120,000 years ago.
Reykjadalur Hot Springs may be visited all year round including winter, but keep in mind in hiking in the winter is much more demanding. The most comfortable season is summertime.