The train offers two classes, first and second. If you're very sensitive to the heat 1st class is your best bet as it is air-conditioned. 2nd class however is still very comfortable, and offers fans in each car. The temperature also gets much cooler once you’re in the mountains. The price difference isn't too much, by Western standards, but first class sells out very quickly.
Occasionally first class will also include a viewing car with giant windows stretching up to the ceiling. These cars don't run all the time and cost a bit more. If they're not running a viewing car you can still get a great view of the ride, if you're willing to take a few risks. Many of the trains doors in second class are left open, and poking your head out on your journey is very easy to do. It can be a bit dangerous, but the views out of these doors are completely unobstructed.
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