Construction is slated to begin in 2014 on what will be the first floating apartment complex in the world. Designed by Netherlands-based firm Waterstudio, the Citadel's 60 luxurious apartments will be built in a polder -- low-lying land -- that will be flooded once the complex is built. The residences will be constructed around a central courtyard, whose main deck is made from a "floating, heavy concrete base." Each unit will have its own green roof, and a bridge will connect the complex to the mainland. The project will use 25% less energy than those built on land.