Welcome to the Chicago Water Tower, one of the most surprising sights on Michigan Avenue. You are on the Magnificent Mile, surrounded by glass, steel and shopping crowds. Right in the middle sits a pale yellow limestone tower with turrets and battlements, looking as if a storybook castle had wandered into the city. It stands in a small park near the corner of Michigan Avenue and Pearson Street. It was never a castle, of course. It was a piece of civic plumbing, finished in 1869 to hide a tall standpipe, a vertical pipe 138 feet high, that helped keep the city's water supply steady. Over the next few minutes we will look at why Chicago needed it, who designed it, how it earned its place in the city's story, and what you can still do here today. Take a moment to look up at the pointed turrets and the rough, golden stone. Then keep that image in mind, because every detail of it is tied to a very practical problem: how to bring clean water to a booming city.