Millions of Chinese cram onto trains to make the annual pilgrimage home for the Lunar New Year holiday. It's a crowded and often uncomfortable experience that is rapidly being transformed by the country's push into the world of high-speed rail.

China already has the globe's longest bullet-train network, but it's plowing 3.5 trillion yuan ($556 billion) into expanding its railway system by 18 percent over the next two years, to 150,000 kilometers, or more than 93,000 miles.

Much of that will be spent on extending the high-speed network westward, which includes parts of the country that ancient Chinese poet Li Bai once lamented were so mountainous that getting there was as challenging as reaching the sky.