Took a lot of reading to get to an explanation:<p>> <i>With the help of a few geothermal experts from Iceland, Black sunk a borehole into the murky depths of the old High Main coal seam in Gateshead, Tyne and Wear, England. Warmed by natural geological processes, the water they pumped to the surface was a pleasant 15C (59F).</i><p>So basically the water-filled mines are conducting geothermal heat.