Geothermal energy comes in three varieties.

The first and most widespread is low-temperature heat—found everywhere, just below the surface—which can be used to maintain a constant temperature in buildings.

The second is much rarer: extreme heat found near volcanoes and fault zones, where high temperatures from deeper within Earth come close to the surface. These can produce steam to run electric power plants.

We’ll talk about both these types on future EarthDates.

The most commonly used geothermal energy, though, comes from hot springs—where rainwater seeps down into the Earth to reach deeper heat sources like magma chambers, then rises back out.

We’ve bathed in, and built around, them for thousands of years, often assigning them religious significance or health properties.

Romans constructed hundreds of baths at natural hot springs across Italy, often featuring elaborate architecture and plumbing systems, and they became an integral part of society—places to conduct business, politics, or courtship.

When the Romans conquered Europe, they expanded upon baths that earlier peoples had built in France, Hungary, Germany, and England.

Today, bathers still enjoy these and other hot springs. While more modern uses include heating houses, pasteurizing milk, and melting ice off streets.