These odd natural formations -"hiidenkirnu"- are rare but here you can find 20 of them and they are potholes in rock. The largest one is over 4 metr in diameter and over 10 metr deep with a spiral like formation in the inner wall. The potholes were formed during the last ice age for more than 10.000 years ago by the shere force of ice, water and grinding stones. Some grinding stones are still in place. The potholes were first found in 1950 and the area was opened to public just 40 years ago.
The area (and even the path there) is extremely rocky and I recommend that you take your best trekking shoes. A lot of steps and stairs to climb.