From Puerto Varas in the Lake District, there's a train to Temuco, north of the Lake District. The city has a railroad musuem with steam locomotives from the early 20th century. Then the railroad continues to Chillán and Talca, in the Central Valley. Once in Talca, you can relax and see the vineyards, and then ride the train to the coastal town of Constitución for an enjoyable overnight side trip. Then continue aboard the train to Santiago, stopping in the wine valley of Colchagua for some wine tasting. In Santiago, be sure to check out the Quinta Normal railway museum. Show Less
There is also a train from Calama in northern Chile to Uyuni in Bolivia, but this is an overnight train so it is not scenic, and it is not very comfortable. We generally recommend private transportation between the Atacama Desert and Uyuni.