Well thanks for the suggestions so far. I wasn't originally planning on going to the Cape on my Boston trip, but thought it would be cool to run a race in that area. I figured I would rent a car, get there early in the morning and run the race, and then hit up the beach for the rest of the day. I can't have a shower or anything (unless there are public showers in the area), so that is why I figured a day at the beach would be a great race follow-up. I might also drive around and visit some of the idyllic villages in the area (I'm from Texas, so scenic cities next to water is a foreign concept for me).
I guess I am just wondering what are the "best" spots to visit in that region. I am going by myself, so I would like to avoid beaches that only attract families or senior citizens.