Lake Michigan is very vibrant, especially around the summertime. The Navy Pier is an extension of this, and I actually went there Labor Day weekend in 2003 for the first time.
There is fun for the whole family. First of all, the pier overlooks the lake, and it is nice to walk and enjoy the music, food, and other activities there.
My wife and I took a Ferris wheel ride there, and we admired the Chicago skyline and the evening lights from high above. They also have a mall at the end of the strip with vendors, ice cream, and other shops.
It is lots of fun, and often in the summer you are treated to a firework show. You have to love fireworks over the water - always nice! Make a point to go here, as it is easy to get there and everyone knows where it is.