Total Immersion
Photograph by Brian Skerry

Like an underwater RV, the Aquarius habitat lets half a dozen scientists live some 50 feet (20 meters) beneath the sea's surface five miles (eight kilometers) off the south coast of Florida. Normally scientists can only visit this world on short dives from the surface. As aquanauts, they spend up to nine hours a day conducting research in the water. In the end, though, they pay for their stay: During their final 16.5 hours the habitat becomes a decompression chamber that gradually reconditions them to live on dry land.