It is completely valid to wonder - infrastructure?! I know, its not the first thing folks are generally interested in. One of the selling points of my current apartment is that I can hear both the freight and commuter trains at a politely demure volume from the comfort of my sofa. Another selling point, of both my apartment and the city of brotherly love, is the Schuylkill [pronounced skoo-kill] Banks park. Not only can you enjoy the beauty of bridges, tracks, boats, bikes, and the like - but its also a scenic park that has a trail extending 22 miles, for those diehard bike and running enthusiasts.
Here are some images as evidence:
Should you ever find yourself on this path, wander along it, enjoy it and take a few minutes to stand under the Market Street bridge. It is here that you will see a pleasant bit of graffiti as well as be able to hear the subway and trolley lines that run underground. The bridge has two air shafts that serve the underground tracks. This is an amazing spot - you can see the cars on I-76, and on the local roads, hear the Amtrak and SEPTA regional trains across the river, and hear the subterranean lines as well. It is a smörgåsbord also known as city - it is what has made it possible and keeps it going - it is a small part of the big word that I love: infrastructure.
Just a tidbit - Philadelphia was once an engineering tourist destination for its waterworks, which is now a lovely restaurant and scenic vista along this very river park.
More pictures from the Schuylkill Banks park and much more are available here