The best train journeys in the world have an intangible allure about them. Since the dawn of time, the romance of railways has seduced poets, spellbound novelists, and dealt directors the perfect hand for capturing fleeting friendships, illicit affairs, and all manner of crimes and capers. A ticket is not just a permit to ride, it’s permission to trespass on the intimacies of other people’s lives. Trains bring us up close and personal—both inside and outside the carriage. On board, passengers chat politics in Finnish dining cars, clamber into couchettes above strangers on the Trans-Siberian, and share samosas on India ’s many raucous mail trains. Outside, the world flashes by, a slideshow of rivers growing into oceans, deserts rising into mountains and cities sprawling then receding into darkness as the train thunders on through the night. As climate change takes hold and travelers look for slower, more conscious ways to move through the world , trains are returning with renewed vigor.…