I'm now living in the north of France (Pas de Calais), an old industrial area with coal mines. So at several places one can see these spoil heaps, made of waste accumulated over years of exploitation. On most of them, nature is coming back, and they are changing in leisure areas for hiking, biking and tourisme. I'm still surprised and impressed everytime I see one , turning around a corner, or passing by on my way to work. : )