On the way back into Reykajavik from Selfoss Stephen and I stopped at the ON Geothermal Exhibit at Hellisheidarvirkju, which was certainly one of the most interesting and educational things I did in Iceland. https://www.tripadvisor.ca/Attraction_Review-g315849-d4358856-Reviews-Geothermal_Exhibition-Hveragerdi_South_Region.html
Hellisheidarvirkjun (or Hellisheidi) heat and power plant constitutes the largest power station of Iceland and the second largest geothermal power station in the world.
Among the many interesting things we learned that 26% of Iceland’s electricity comes from geothermal. There are many other uses for the water, including home heating, showers etc,but also being distributed under the roads and sidewalks to melt the ice in the winter, before the used water is pumped back into the ground to maintain pressure of the geo-thermal sources for future use. Much of the geothermal water pumped from as deep as 2,000 metres (yes that is 2 km!) is too hot and toxic to be used in bathrooms so that water is used to heat clean surface or close-to-surface water which is safe to pump to Reykjavik for residential use.
Hellisheidi is only a couple of hours from the capital so it was an easy drive from there into Reykjavik from whence Stephen was leaving the next day on the same plane as Laura was arriving.