We got in for free since we we were camping in a state park nearby - always a plus! It was my son's first beach experience and the water was not too cold. The sand was clean, but the shore was rocky. Also, lots of seaweed! We went mid-August and it was suprisingly not too crowded - another plus.
Located between Waquoit Bay and Vineyard Sound, South Cape Beach is part of South Cape Beach State Park, which has several nice nature trails. The beach is the attraction here, though: It’s a 2-mile-long white sand barrier beach with a bathhouse, a snack shop, and a big parking lot that rarely fills.
The park is jointly managed by the State of Massachusetts Department of Environmental Management and NOAA, which oversees the Waquoit Bay National Estuaries Research Reserve (of which South Cape Beach is a subset).