Anyone know of a beach between baltimore and the lehigh valley? Or one that's not too far out of the way?
I assume you don't mean an Atlantic Ocean beach; any of those would take you quite a bit out of the way.
There are public beaches on the Chesapeake Bay: baydreaming.com/chesapeake-bay-living/…
The beaches on the bay are all well east of Baltimore, Sandy Point probably being the closest. The only "beaches" you will find between those 2 areas will be on lakes. You would have to look for lakes between the 2 and see if there is a public beach. You will most likely find public access at state parks.