This is the famous Chicago Water Tower. It, and the pumping station next to it (you can't see it in this photo) were built in 1869. The tower was the only public structure within the burn zone to survive the Great Fire of 1871.
The tower is 154 feet tall, and contains a 138 foot standpipe used to help with water flow and pressure for the pumping station. Both the tower and the pumping station are still in use today.
I think it's beautiful - this castle tower in the midst of what is now a city of steel and glass.