Westminster Junction
A companion and I were able to take some time to visit Westminster Junction in St. Paul, Minnesota. What is unique about Westminster Junction is that it is one of the only places (or maybe the only place) in Minnesota where urban train tunnels exist. They were put in to help aide in traffic management of multiple lines crossing near Swede Hollow.
Two great locations to view the junction and the tunnels would be from the Phalen or Lafayette bridges. The Phalen bridge actually has a marker describing the history of the junction.