Running around Baltimore's Inner Harbor, say around/over Federal Hill & over to Ft. McHenry, is a great run....altho' prolly not so much in the winter. Plenty of well-placed benches for resting along the paths at the fort, incl. one that explains what all the various marine horns, boat horns, channel lights, etc. mean.
If you're really in for a cardio blast, the "steps" up to the top of nearby Federal Hill make a good challenge.

If you need a good "gym" possibility, another Baltimore Sheraton, the Sheraton Baltimore North up near Towson gives its guests free day passes/access to the Bally's down the street.

And, as a Plat, their Club Lounge has a decent selection of appetizers, o.k. beer & wine--evenings, decent continental breakky options in the a.m., a manager's cocktail party on Wednesday evenings, and very helpful & friendly club lounge staff.

It's in a much better general area than that surrounding the Sheraton Inner Harbor---you can walk around a few blocks from the hotel and not feel the need to know where the nearest police are, where the blue-lighted surveilance cameras are, etc. Right at the Inner Harbor, Federal Hill, JHU...all cool. A few blocks away? Scary.