One day our society could run out of building room, the land so overpopulated that the only place to turn for expansion is the water. It’s alarming to think about, but Naval designer Giancarlo Zema’s Trilobis 65 — a floating habitat sufficient for six people — could very well be the home of the future. Each floating home consists of four stories (two above water, two submersed), all accessible by a central spiral staircase. Check out the Web site for more specific details.