We got an exclusive look inside Fisher Island's largest penthouse, and it just so happens to be up for sale. The five bedroom, five and a half bathroom unit, which is listed by Douglas Eliman's Pablo Alfaro and Cyril Matz, has almost 10,000 square feet and boasts expansive views of the bay, has a library, an in-home gym and the latest in technology. But living in one of the United States' most exclusive and most expensive zip codes comes with a price. The unit is $21,000,000.