This stone is not man-made, is river-made. Stones like this are very usual in many rivers in Colombia. They come in all sizes, from about 10 cm in diameter to around 2 meters.

My family used to have a summer house in a little town called Utica, Cundinamarca. Around the main place there are several of these rocks in different sizes, one of them about 1.3 meters tall, holding a big lamp post.