Strange rocks and human imagination have been deeply linked since the first Homo sapiens squinted at some weirdly-shaped peaks and wondered why they looked the way they did. In the millennia that have passed since then, natural rock phenomena have been turned into shrines to pagan deities, Christian saints and Muslim sages. Legends, often bloody and brutal, have been invented about their origins.

The Stone Mushrooms, near the Rhodope village of Beli Plast, are a case in point.

What you see when you stop your car and walk the short distance to the phenomenon is a group of rocks that indeed resemble mushrooms. The most spectacular of them rises up to 2.5 m. According to geologists, the phenomenon is the result of underwater volcanic activity, combined with erosion when the sea, which used to cover most of what is now the Rhodope mountains, withdrew.

Ask a local, however, and you will hear a hair-raising legend.

Here is how the Stone Mushrooms came to be.

Once upon a time, a local Bulgarian charcoal burner had four daughters. One day, they went to fetch water. On their way, the girls stumbled upon a group of Ottoman invaders. The girls ran, but the invaders' leader pursued them on his horse and eventually caught up with them. The girls, however, did not act like meek victims. They resisted. They surrounded the attacker's horse and startled the animal. When the man fell, they fell upon him, tearing him apart with their bare hands.

This act of insane bravery did not save them. The dead man's best friend soon caught up with them. He drew his scimitar, attacked a girl and cut her head off. But then something miraculous happened. When the head hit the ground, it turned into a rock mushroom. The same happened with the second girl's head. And with the third. Amazed, the man dismounted his horse. He lowered his scimitar. But the fourth girl's head still fell to the ground, becoming a rock mushroom as well.

Terrified, the man hopped on his horse and gave it a start. But he never left the place: after just one step, he turned into a black rock. Locals today call the lonely rock that stands by the mushrooms Karatepe, or Black Hill.

The Beli Plast, or White Layer, nature phenomenon has also become the stuff of a newer legend. For some reason many people now believe that its zeolite rocks have almost magical healing powers. Supposedly, you only need a chunk of it in your drinking water.