Along Þjórsárdalur valley lies the road leading to Landmannalaugar and the highland center Hrauneyjar as well as Viking age farm Stöng which has been restored after being excavated in 1939. Mount Hekla is located in this area and is one of the more active volcanoes in Iceland regularly spewing out volcanic ash and lava flows and believed to be the gateway to hell in medieval times. The Hekla eruptions have been quite numerous and on average the volcano erupts every 10 years, the last major eruption was in 1947, but it has now been almost twenty years since the last one so everyone is waiting excitedly for the next one, of course the longer we wait the bigger the bang.
Þjórsárdalur valley has entered popular culture recently through the Game of Thrones tv series which feature backdrops from this area and it is especially recommended to check out Hjálparfoss waterfall which is a stunning spot where the river is split in two as it tumbles off an ancient lava flow. There are some day hikes that can be done here and it is a good idea to check out a hiking map detailing the safe routes.
When going through Þjórsárdalur towards Fjallabak Nature Reserve and Landmannalaugar you go through Laugahraun lava field among others and there you find rhyolite mountains as well as the Blue Peak. There is quite a bit of construction here in connection with hydroelectric power production, a reservoir and a deep canal, using the plentiful glacial water to produce power for the area as well as supplying to the national grid. This is also one of the few places that windmills have been set up and surprisingly wind power is only at an experimental stage in Iceland.
There are some natural hot springs here although the biggest ones are in Landmannalaugar. The area is very much a product of being on the mid atlantic ridge and in fact Þjórsárdalur has a large portion of one of the biggest lava flows from prehistoric times that have ever been discovered. Þjórsárhraun Lava Field formed during a massive eruption some 8600 years ago in 6600 BC and covered a vast area around 130 km from its source from the Veikiðivötn area in the interior of Iceland all the way out to sea and is estimated to be around 970 km2. Parts of this lava flow can be seen on the banks of Ölfusá river and Þjórsá river but a lot of it has been covered by latter day minor eruptions as well as having been buried underground. On the coastline by the towns of Stokkseyri and Eyrarbakki you can check out where the lava entered the ocean and pretty much stopped there although highly eroded it still be made out. There are of course various major eruptions which have affected not just Iceland but the rest of the world. Around 1200 BC a Hekla eruption spewed so much ash into the atmosphere that it affected the climate in the northern hemisphere and caused the demise of some cultural pockets in Europe. Then there is the great Lakagígar eruption which created Eldhraun the earth´s biggest lava field of historic times around 600 km2 or roughly the size of the city of Chicago, and the ash cloud resulted in very harsh winters which caused a famine in Europe which in turn sparked the french revolution. So, Icelandic volcanoes are not to be messed with.
Icelandic touring can be a lot of fun and it is well worth reading up a bit on the various places to see. Whether you want to do mountain huts and sleeping bags or find a comfy hotel with a geothermal spa and cozy bar, there is always some way of catering to your needs.