The first railroads in the United States were engineering marvels built to conquer America's deadliest places. Using cutting-edge science, engineers and builders changed the nation by connecting the California frontier with the rest of the country.

Experts use cutting-edge tech and bold engineering to build a record-breaking bridge that spans a deadly chasm in a remote section of the Himalayas. When completed, it will be the world's tallest railway bridge, towering almost 1,200 feet high.