In 1918, New York City’s then-mayor, William Russell, had a 17-room mansion constructed for his daughter on an island in Islesboro, Maine. Known as Grace Estate, the waterfront property, now valued at $9.5 million, sits alone, surrounded by Penobscot Bay. To get to the massive home, you must take a 20-minute ferry. At 9,000 square-feet, it features eight bedrooms, a modern kitchen, pool, putting green and a deep-water dock. Learn more about Grace Estate.