The technology underground is a thriving, humming, and often literally scintillating subculture of amateur inventors and scientific envelope-pushers who dream up, design, and build machines that whoosh, rumble, fly—and occasionally hurl pumpkins across enormous distances. In the process they astonish us with what is possible when human imagination and ingenuity meet nature’s forces and materials. William Gurstelle spent two years exploring the most fascinating outposts of this world of wonders: meeting and talking to the men and women who care far more for the laws of physics than they do for mundane matters like government regulations and their own personal safety.