Since Xiahe is located in the southwestern part of Gansu Province, whose train lines run northwest to southeast, there are no railway lines anywhere close to Xiahe or the neighboring  area. To get to Xiahe from Xi-an you need to get an overnight train to Lanzhou and then drive for 7 hours. There doesn’t seem to be any local transport to this area and you need permits to get there but there may be a local bus. The train from Xi-an is comfortable but not as nice as the one that runs from Beijing to Xi-an. There are different classes (hard and soft sleeper) with the hard sleeper having 3 bunks on top of each other (6 to a compartment) and soft 2 (4 to a compartment). They do sell food and drink on the train but I’d recommend to bring your own snacks.