The exact cause of the fire is unknown, but it was probably a case of
spontaneous combustion caused by pressure and decomposition as a result of unplanned
coal mining. According to legend, a shepherd lit a fire at a tree stump, which propagated down through the roots to the coal seam. An unsuccessful attempt was made to fight the fire with water. It does not burn with an open flame but instead glows. Originally this glow could be seen through cracks in the rock and there was a considerable build-up of smoke. The fire began to weaken by the end of the 18th century. Depending on the weather, smoke is visible and in at least one of the rock crevices an outflow of warm air can be detected. == Tourism ==