Driving through Hellisheiði the hillside you drive when driving from Reykjavík to Hveragerði. Is a well known outdoor activity area for the capital area. Around this area, you will find nice hiking and biking trails making this a popular area for locals to go out and enjoy outdoor activities.
There you will find the Bláfjöll area, which is the biggest ski area in Iceland, even though the area is quite small and with a low mountain, it‘s better than nothing. Around the Bláfjöll area, you will find lava fields, with caves and lava tunnels. The most famous one is Þríhnjúkagígur which is an enormous magma chamber, it‘s the only magma chamber in the world that can be entered. Only possible going there with a tour operator, then you get lowered down with a lift. The tours only run in the summertime.
Hellisheiðarvirkjun is a power plant, a geothermal power plant providing electricity and hot water for space heating in the industrial and domestic sectors in Iceland. They make energy by drilling deep holes into the ground, they can find water up to 300°C in temperature. When the holes are opened the water boils out of them creating warm steam on the way out. The steam is then separated from the water and use to power some of the plant‘s turbines. Then the rest of the water is depressurized and use to make more steam. The maximum output of the station can produce about 303 MW of electricity. This steam is also used to heat up cold water to make hot water for the capital area. The pipes you see along the road are used to transport this hot water to Reykajvík area, where it‘s kept in large water tanks, they only manage to cover half of the capital area with that water, the other half comes straight from the ground and therefore contains more of silicon dioxide (SiO2), causing the smell you might have smelled while showering in Reykjavík.