True Duplex penthouse condos (no one living above you) are rare; there are currently only 12 listed. Not only is this the least expensive, but the average cost of the other 11 is almost double that of this listing. This is not because this one is a slouch-quite the opposite.

To begin with, it boasts the best view of all, but there's much more to it. At 2,500 square feet, this true penth...