It's a rock. A very old rock. But then almost all rocks are very old. The difference is that this one was carved & put there thousands of years ago.It doesn't look much like one of Obelix's, though.
Menhiry : [4]. Dolní Chabry, obvod Praha 8 (Zkamenělý slouha) - Chaberský menhir si určitě nenechte ujít. Je vlastně jedinám dochovalým menhirem na území Prahy.