People around the world guzzle about 50 billion gallons of bottled water a year, and then toss billions of those plastic bottles into the trash heap instead of the recycling bin. Matt Naples and Peter Zummo think they can take this lemon of a fact and turn it into lemonade—or rather, take those discarded water bottles and turn them into chairs, shelves, or houses for the world’s poor.

What will San Francisco look like 100 years from now? According to the winning entry in a "city of the future" contest, residents will live in a forest of sinuous towers.

IwamotoScott Architecture took home the $10,000 prize for its "Hydro-Net" design, which also envisions an underground web of carbon-nanotube-walled tunnels where people travel in hydrogen-fueled hover-cars.

If solar power and recycled building materials just aren’t green enough for you, the brains behind the Fab Tree Hab might have the perfect pad. Architects Mitchell Joachim and Javier Arbona, along with environmental engineer Lara Greden, have designed a house that will grow from a few seedlings into a two-story, water-recycling, energy-efficient abode. The Fab Tree Hab,
a mix of ancient and ultramodern technology, isn’t
merely environmentally friendly.

What happens to airplanes when they die? Though it's fun to imagine them flying up to some big hangar in the sky, the truth is that of the 200 that are retired worldwide every year, most end up in scrap-metal graveyards. Some are even simply abandoned to rust next to landing strips, becoming the FAA equivalent of junked front-yard jalopies.