Even though there's sand underfoot in these pictures, the surrounding area is tree-dotted meadow. The "forest" runs about three kilometers by half a kilometer and a road straddles it. They say these rock formations were made just like stalactites and stalagmites and then the cave just fell in and eroded around them while they stayed in place.
The guide/money collector (entrance was less than two euros each) gave us a New Age spiel about the energy of the rocks and their spiritual healing power. Needless to say, we didn't fall for that. We did, however, take lots of pictures of lizards and flowers. Those aren't on flickr yet, though. Anyway, if you get to the Varna area, do visit. It's impressive.