Swiss Rail is known by many for its proverbial punctuality. Having travelled a bit by train in Switzerland, though, to me another feature is the most striking one: It's reach. Swiss trains climb most mountain chains to reach even small rural valleys and remote towns in the backwaters.
Where in most countries trains and public transport in general are a travel option for the less affluent, Swiss Rail to this day seems to be the national mode of travel for all strata of society. Just check out how many Swiss own a GA (General Abonnement), a full year rail pass, costing 3800 CHF in 2nd class.
In a country so infatuated with railways I think the inclusion of the single most iconic railway of the country is a worthwhile addition.
How to Visit
I have to concur with previous reviewers' statements: It's a bit hard to appreciate the site from the train window. While you get nice views of the scenery, you don't see much of the engineering feats. However, you can hop on and off the train and hike from one station to another. There is yet another Swiss heritage trail running from Thussis to Tirano that you can join at any station.
I only covered a small portion of it at Filisur but it included the famed Landwasser Viaduct. If you have some time (I didn't) I would probably hike from the Viaduct to Bergün where the Albula Train Museum is located. The museum is rather pricey (15 CHF) for a rather a small site, though.
Getting There
Most train aficionados will probably opt for the Bernina Express from Chur to Tirano via Sankt Moritz. This is also the most pricey option as you need to pay additional reservation and booking fees, also payable by holders of the Swiss Travel Pass. Alternatively, you can take the normal regional trains running the area. These seem to run every hour and are free for holders of the Swiss Travel Pass.
While You Are There
The end point of the line in Italian is Tirano which connects you to the Milan Hotspot.
From Sankt Moritz / Samaden you can go to Müstair. First take the train to Zernez and from there the bus to the abbey. From Müstair you can also head into the Dolomites.
Via the capital of the region in Chur you can travel back to the Zürich Hotspot. You also have access to the Swiss Tectonic Area Sardona via Flims.