Buildings in the Lower Manhattan skyline are reflected in a puddle at Main Street Park in the Brooklyn borough of New York, U.S. (Photographer: Michael Nagle/Bloomberg)

For $13 Million, Two Private Islands 30 Minutes by Boat From Manhattan

(Bloomberg) -- It’s hard to give the exact dimensions of Columbia Island, a small piece of bedrock off the coast of New Rochelle, N.Y., because the tide changes its dimensions so dramatically.