Walking under the bridges along the Riverwalk in Chicago provides a very different perspective that that which you get from above.  Some of the bridges have solid deck and others have gridded metal decks which allow light through (and anything else someone might drop).  The lattice structures under the deck are ornate yet grubby.  They are obscured from most views and get covered in the grime that washes down from above.  I am not making this sound very appealing but I find them very cool to look at.  The noise of the traffic above is there but slightly isolated which adds to the atmosphere for me.  They do put a curved stainless-steel cover over the walkway itself so you are not vulnerable to anything from above ending up on your head which is something I am grateful for.