The United Arab Emirates knows that the oil isn't going to last forever. Its prime minister, Sheikh Mohammed, is also the Emir of Dubai, and he has spent the last two decades working to turn his city into a world-class tourist mecca that can survive without petrodollars. But many of his challenges have been geographic: there's only so many miles of beach on the Persian Gulf. It's not easy to add hundreds of miles of coastline to a crowded city, but that's exactly what Dubai is trying to do—by building the world's three largest artificial islands.