The “L” is Chicago’s transit system. The name comes from the fact that a large portion of it is an elevated rail system.
Here are some pictures from the ride back from downtown Chicago to the Howard station on the Red Line. The first picture is the pavement right near the entrance to one of the L stations downtown. The second picture is on the side of a school building, and I’d guess it was a catholic school. The fancy building in the third picture is the Aragon Theater.