I went on that shoot today that I will be supervising the sound of.
We were in an L.A. metro station. (BTW did you know it costs about $20,000 for a shooting permit in a subway?? I'd rather buy microphones and shoot everything inconspicuously on a Canon 7D or something... Anyway, I digress)
Coming down the escalator I noticed it made an awesome rhythmic mechanical sound which could be pitched down and used as a large machine or some other contraption that has a rhythm to it.
I'll upload some later when I get a chance, but whenever you're around escalators with a mic, I suggest sitting at the bottom of one and record very close-miced to the steps going under - it sounds awesome.