First built in the 1950s, the iconic green trains are a relic of another age, differing in almost every way from the sleek high-speed rail cars replacing them. Tickets are dirt-cheap. The carriages are crowded, chaotic, and stifling in the summer heat. It can take hours for the lumbering locomotives to chug between cities. Yet Qian can’t stop riding. Since 2006, he estimates he’s traveled 150,000 kilometers by “green train,” accumulating 490 ticket stubs and 200,000 digital photographs along the way.