I was there two months ago searching for the traces after prehistoric shrine, which was found in 60s. BTW it was really exceptional discovery. It is very special sacral object and burial place of apparently very important priestess or witch, because of abundance jewelry. In this place was also discovered fallen menhir, but this stone was transfered to the yard of the archeological institute in Prague. (For the details check the topic "Libenice Stela").
The stone on the picture next to you is very new and is made of concrete. It is the modern artwork, made on the cost of Libenice office to commemorate this ancient history. The true is, that except this new menhir there is nothing much to see there. I hope Rorothy has the answer now:-)
Something is not right. This message is just to keep things from messing up down the road