Mother Earth is a hot planet. In a depth of around 6.000 km the temperature could be around 5.000°C. One third of the energy stems from changed gravitational energy in the early earth-creation-process and the bigger part from natural radioactive processes until today. Geothermal Energy has a big potential and is already used in many countries since decades. Its useful resource is divided into surface-near (down to 400m) and Deep-Geothermal Energy (400-5.000m). For its use are a lot of technologies available. In the picture we see a combined condensation-/binary cycle power plant. It produces heat and electricity for private and industrial purposes. The warm waste-water flows into a bassin, the "Blue Lagoon", which is used for balneology and tourism. For further information about the topic please visit, e.g.: https://www.irena.org/geothermal or https://www.nationalgeographic.org/encyclopedia/geothermal-energy/ or https://www.power-technology.com/features/what-is-geothermal-energy/ or https://www.environmentbuddy.com/energy/geothermal-energy/20-amazing-geothermal-facts/ (last visit: 2022-01-11).