The Stone Mushrooms (in Bulgarian Каменните гъби) is a group of volcanic tuffs located near the village of Beli plast, next to the road between the towns of Haskovo and Kardzhali. Their forms resemble mushrooms, hence the name.
The destination can hardly justify the long journey required to visit it, but if you are travelling in the area (maybe to visit Perperikon), why not spend a couple of minutes to stop and enjoy its beauty?