It’s an abandoned slagheap of an ancient coal mine. It consists of rocks of various colours raging from grey to pink.
It is difficult to rehabilitate an area after a mining extraction. In the region of Borinage, numerous abandoned slagheaps remain. Bit by bit, these can become re-covered with vegetation thanks to human intervention: we can see these mountains of stones in many places. Joris says that they were installed there for the animals to take refuge. Shrubs have been planted. If we leave nature to do its thing, the natural reforestation could take 70 to 80 years.