An architecture firm in the Netherlands, Waterstudio, specializes in architecture that "makes friends with water." Its principle designers are environmental futurists, attempting to create structures for a world where water levels are much higher than today. One of their projects, which will be completed this year, is a floating mosque in Dubai. See the interior, and another concept for a floating mosque, below.
Daniel Dociu drew the amazing floating mosque below as Guild Wars concept art, and you can buy a print of it here.
Floating Mosque [Waterstudio]