Paolo Soleri, who died last month at 93, transformed the way people imagine cities of the future. You've probably seen some of his concepts without realizing it. He even built an experimental city in Arizona, called Arcosanti. We've got a gallery of his drawings and designs, some of which have never been online…

The history of rapid-transit began 150 years ago, with the opening of the Metropolitan Railway in London in 1863. In the next century and a half, dozens of architects and engineers have worked on underground tunnels and stations. Some are abandoned now, but others are as good as new. Here are some of the most…

Looking for an alternative to turbines for capturing wind energy, Belatchew Arkitekter has proposed adding a hairy addition to Stockholm's Söder Torn. It would serve as more than an architectural toupee, capturing energy through the movement of all those tiny straws.

The Olympic Games are always proceded by a furious amount of building as host cities construct arenas, pools, ski jumps, Olympic villages, and anything else the games demand. While some of the buildings are repurposed after the athletes depart, others are left to rot.

Forget putting up four walls and a roof; these homes use the stony walls of natural and human-made caves to shelter their inhabitants from the storm. Check out these incredible rocky homes, from ancient cave dwelling to modern house, to the buildings that may have inspired J.R.R. Tolkien's Hobbiton.

Some of the world's greatest architectural wonders don't feature straight vertical lines or cool curving silhouettes — there are leaning towers all over the world. Some of them were built that way, and some have just started to lean over time. Here are some of the most eye-popping photos.

Elysium, Neill Blomkamp’s long-delayed futuristic Matt Damon vehicle, tells the story of a class war between the unwashed masses, who live on Earth, and the super wealthy, who live in an absurdly opulent community in the sky. And as it turns out, the super-luxe buildings of Elsyium's tomorrow actually exist right here …

Bridges are the lifeblood of cities. They bring people and goods into towns, sustaining the vital center. But bridges are also a major engineering feat, and towering works of beauty. Here are some of the world's most inspirational bridges.

While some pieces of conceptual architecture guide out imagine toward distant planets, others plunge us into the depths of the ocean. These underwater cities concepts, dreamed up by illustrators, architects, and designers, imagine the sorts of structures we might inhabit beneath the watery surfaces.

While some architects prefer to take more subtle cues from the natural world, others go whole hog (or sheep or elephant or cat) and make grand structures shaped like animals. From a kitty kindergarten to a whale of a house, here are some of the more spectacular examples of animal architecture.