Cheonggye Stream, which flows through the center of Seoul, is a popular place to relax. Its clean water is home to many birds and fish. But just 12 years ago, it was an eyesore. Its polluted, filthy water was more of a trickle than a flow. Now, 10 years after it was completed, it's an internationally recognized regeneration project.

Scientists are at work deep in the mountains of central Japan. They hope to prove a theory of Albert Einstein's. Two hundred meters underground, inside an abandoned zinc mine, the researchers have laid two pipes in tunnels at right angles, each three kilometers long. The tunnels are so long it's impossible to see light at the ends. The tunnels are also so long that on this job, the scientists move around by bicycle.