Sometimes I get questioned as to why I would spend so much more for a lens with a faster (smaller) f-stop. The answer is creative focus control. If you want a certain image to just pop or draw the viewers attention to a specific area of the image, try using a smaller f-stop. Sometimes you want the whole image to be seen in focus, but you run the risk of creating a snapshot and not a possible piece of art; make that decision before you click and you will be much happier with your photography.
Not a place you really want to go alone; though I did. I would love to go back and shoot some more HDR in these conditions as they lend themselves so well to the process, but there too many eyes looking out from behind pillars and under boxes for my safety to be ensured down there. They were probably mostly harmless addicts and homeless, but my comfort zone shrank considerably in just a few minutes.