dutch valley with a pond and the limestone cave duivelsgrot devil`s cave in sint-pietersberg

autumn caestert cave cavern caving creepy day devils duivelsgrot dutch earth entrance environment erosion europe explore formation geologic geology grotto ground hill hole holland landscape limburg limestone maastricht marl mountain mysterious nature nederland netherlands nobody opening part plateau pond quarry reserve rock sand scenery scenic sintpietersberg slope south speleology stone surface texture travel tree tunnel underground underworld valley velvet view vineyard wijngaardgroeve winter