The Citadel was designed by Koen Olthuis of Waterstudio and includes "60 luxury apartments, a car park, a floating road to access the complex as well as boat docks."
Just a part of the New Water development, The Citadel is also remarkably energy efficient — the water is pumped through pipes in the structure to regulate temperature.
See the full article and more pictures at Inhabitat | The Citadel: Europe’s First Floating Apartment Complex.