I know I've started or participated in a few threads about running at airports. most recently about running at DFW. (I was planning to run at the Hyatt Regency, but ended up taking the day off.) I have run somewhat regularly at BOS, JFK, LAX, and LHR, all of which are easy to do; at BOS, LAX, and LHR, one can run right from the terminal (T5, in the case of LHR), and at JFK one can take the AirTrain to Federal Circle and then head out for a run.

Tomorrow I have a four hour layover at PHL and am considering going for a run. Anyone know what the options might me, preferable outdoors if it's not too hot? And are there showers available at one of the Admirals Clubs or at the BA lounge when I return?