Put on your walking shoes and walk the boardwalk from one end to the other. You can go from casino to casino without going outside in several instances, although the sights you will see while on the boardwalk often make the trip worthwhile. If you get too tired you can always have someone push you along the boards in a wicker (or plastic molded to look like wicker )rolling chair. Stop and buy some (Steel's) fudge and some taffy along the way.
I don't know anyone who has ever walked from the Showboat to the Marina District (Trump Marina/Harrah's/Borgata). Additionally, I would not recommend going past the Showboat at night......
To get from the boards to the Marina District take a Jitney (think bread truck with seats). That is an experience in-and-of-itself and is relatively cheap.
Have fun and good luck!
Best Regards,
Murph