Caritas Island Fairfield County, Conn.
$25 million plus (A$33.4 million, C$28.3 million, €20.8 million, £14.3 million, Rs1.1 billion)
It's a rare luxury to have a private island an hour's drive from Manhattan. This four-acre island is connected to Connecticut via a private road, and features a 14,000-square foot stone manor house, built in 1906 for members of the Phelps Stokes family. The mansion has a marble entryway, herringbone oak floors, marble skirting, a two-story gourmet kitchen and library with a cathedral ceiling. The estate includes a lap pool, saltwater pool, 200-foot deepwater dock, guest cottage, caretaker's cottage and gardens.
Links: www.forbes.com, www.zillow.com, www.your-dream-island.com