Hi, These stones are in the same dere with the waterfall and turtles. Above the stones passes ancient Roman path to North Bulgaria also near I found several very old iron slags.
Those rocks have fractures because of a tectonic movement's effect. These can be seen everywhere. From these photos nobody can say that there is no or yes for a cave behind or under those rocks. on the other hand i can surely say that there is no mine behind these rocks.