I recently took a walk on the 606 with my grandson. What is the 606 you say? Here is some info from the excellent 606 website:

The story of The 606 begins just after the Great Chicago Fire. In their efforts to rebuild the city, the Chicago City Council gave permission for the Chicago & Pacific Railroad to lay tracks down the middle of Bloomingdale Ave. (1800 N) on Chicago’s Northwest side. The move helped connect goods from outlying rail ports to the busy Chicago River, and supported Chicago’s burgeoning industrial growth.

You can read more at the website. If you are ever in Chicago, it is worth taking some time to walk the 606. It was a cold day, but we just loved the sights and sounds of our walk.