Can I assume you have done Mackinac Island?
Look into Ballston Spa/Saratoga Springs, New York. The latter gets its name from the natural springs, so it's sort of like a spa. Make sure to check the racing schedule, though. It will be swarming with fans in August, I think--and totally booked.
I don't remember any names, but I know DH and I went hiking in the area way back when (~20 years ago). There is no beach, of course, but you could check out Lake George to the north.
DS '04 "Boogaboo"
DD '08 "Lilybear"