It just occurred to me that akin to electric power lines, which in the end just connect a voltage differential over a long distance and facilitate power exchange between the two end points, one could build "thermal power lines". That is, a well-insulated cable that internally consists of a material with very high thermal conductivity. This way, one could facilitate energy (heat) exchange over long distances, between two points of vastly different temperatures (e.g. a desert and the bottom of the ocean). Question is, how feasible would it be? It would certainly not travel at the speed of light like electricity, but for heat exchange it probably wouldn't need to. Has something like this been tried before?