In Bulgaria, on the road to the capital of Sofia, is a remarkable natural area called Pobiti Kamani or the Stone Forest. At first glance, it looks like the ruins of an ancient temple, but these broken stone pillars are all natural.
The most curious thing about these pillars is that they are mostly hollow and filled with sand. They don't have a solid foundation or attached to the bedrock. Instead, the pillars are loosely stuck into the surrounding sand as if some one had hammered them into the earth.