Unsolved Mysteries

The past does not give up its secrets easily. Brand-new machines are helping explorers reveal mysteries once thought lost forever. Underwater archaeologists are searching for a World War II Nazi sub that disappeared in U.S waters. In Scotland, researchers are digging up an ancient rock, covered with cryptic markings, that could reveal more about who built Stonehenge. On this episode: German Submarine U-576; Cochno Stone; LIDAR.