The race for green energy solutions has forced many countries to consider the potential of geothermal heat. This approach will require the digging of some of the deepest holes on Earth in order to harness that heat.

Currently, the deepest mermaid hole on the planet is the Kola Superdeep Borehole at a whopping 12.2km deep, but it has its origin in the cold war era, long before people were seriously considering this sort of power.

So, why was it dug?

Mark Piesing is a Journalist & Author who has written about the hole. He joins Seán to discuss.