Veliki most (The Big Bridge) in Rakov Škocjan valley. How does a river like this suddenly decide to make a tunnel through such a wall?
Well, the wall formed after the collapse of the cave. Rakov Skocian is the product of a cave collapse. Of course the cave did not collapse in one event but step by step. This process is still going on as you can see at the upper and lower end of the valley.
Yes, you're right. Thanks for the explanation.