South Cape Beach in Mashpee is a great local beach, albeit it narrow.   There are two parking lots, one which is operated by the State (part of the Department of Conservation and Recreation - DCR) and the other by the Town of Mashpee.  In season, the State Park charges $15 for state residents and $40 for non-state residents, although you can get resident passes at the Mashpee library (and other libraries we suspect).  The Town lot requires a beach sticker in season, which 55 has for one vehicle.  Alternatively, if you don't have a lot of "stuff", you can bike to the beach from 55 in about 20 minutes.

The beach is great for walking, including on a few wetlands trails.  The beach is steps from the parking lot.  It's also handicap accessible and has port-a-potties and, sometimes in season, a snack truck.