Near the village of Beli Plast are the mushrooms - a part of the so-called Kardzhali pyramids. They are natural formations that are millions of years old. Interesting rocks in the form of giant mushrooms, whose height reaches 2.50 meters, the extent of their stump is 8 meters and circumference of the cap up to 10m! The “fungi” are formed 50 million years ago, as the eastern part of the Rhodope Mountains was bottom of the sea. Their formation is a result of volcanic action underwater. After the sea began to shrink, units were exposed to erosion, the base turned prone and the upper piece has proved more durable and resistant, because they were formed from volcanic glass. The rocks have the presence of various minerals, thanks to which they are dyed in a very interesting way - their stumps have a pink hue and hats are green.
There is a strange legend about the origin of the stone mushrooms. It states that the fortress Perperikon a coaler, who lived at the time with his four beautiful daughters. One morning when the girls went for water outside of the fortress, they reached a river, but suddenly they saw that behind the hill a great horde was approaching. They ran back to the castle and later began a heavy battle. The battle was uneven and the enemy captured the fortress. Many men were killed, and women, amoung which the four daughters of the coaler, were caught.
The captive girls were taken to the chieftain of the horde so he could choose for himself the most beautiful and sell the rest as slaves. When the girls came closer, they were overcome with rage and began to throw different things at the leader of the Horde. His horse fell out of fear and the girls fled into the forest.
After the girls went to friend of the leader and he had almost caught them at sunset. He struck out with his scimitar and cut off the head of the girl who turns into a stone sponge. The same thing happened with the other two girls and the fourth turned himself in a stone. The rider and wanted to take flight but, he changed into a black stone and so the people here today call the rocks next to the mushrooms Karatepe (which translated from Turkish means "black hill").