The structure is called the Ahmed III Fountain (III. Ahmet Çeşmesi). This famous fountain was built in front of the Imperial Gates of the Topkapi Palace in 1728, under Sultan Ahmed III. Surprisingly, the fountain is still working. In the sense that the water from the taps is flowing...
I looked at the building, well, it's historic, but I didn't see a fountain. It is necessary to visit with guides, maybe they will tell you something amazing.