Four railway lines, four continents' worth of engineering risk. The Tanzania-Zambia Railway, built starting in 1970 with Chinese financing after the World Bank called it too dangerous, cuts 1,860 kilometers through forests, mountains, and wildlife parks between Dar es Salaam and Kapiri Mposhi; the film notes the project cost 160 workers their lives. In Argentina, the segment tracks lines built across nearly 300 years of engineering history through extreme heights and open savannah. In Peru, the Ferrocarril del Sur climbs through the Andes on one of the highest train routes on earth, linking Cusco, Machu Picchu, Puno on Lake Titicaca, and Arequipa aboard the Andes Explorer. The final chapter follows India's Pamban Railway across the tropical coastline of Tamil Nadu. Each segment mixes on-board footage with landscape cinematography and historical narration explaining how these lines were built and why they remain hazardous, treating the railways themselves as the through-line connecting otherwise unrelated corners of the world.