From The best of Bursa-site I took this explanatory text: "The Swimming Stones fountains on Altıparmak Caddesi [...] granite columns, designed by renowned German sculptor Christian Tobin, represent Karagöz and Hacivat, Bursa’s famous shadow puppets and unofficial ambassadors. In this sculpture, water flows out of the joints between the two stones in each column, with the upper stone rotating on top of the stationary lower stone. This is a kinetic water sculpture, which means that the 7- and 8-ton upper stones are not connected to the lower stones. The upper stones rotate freely by the force of the water welling up into the joints between the stones, yet the stones remain stacked by gravitational balance. "