If, like me you're looking for waves and the actual ocean, rather than the harbor or an inlet, the closest I have found is Revere Beach in Revere. If you're taking the subway you simply get on the orange line or Red Line in Bound and then switch over at State for the blue line. That will take you all the way to Revere Beach stop. You litter We Walk off the Earth Subway and the beach is right in front of you. Clean, usually quiet, plenty of places to park, and Kelly's Seafood is in the area.