Cross the Alps on the Bernina Express
Make the train journey between Chur and Tirano the occasion, while choosing deliberately between panoramic and regional services.

A train journey becomes something different when arriving is no longer its main purpose. Crossing from Chur to Tirano on the Bernina Express is a chance to give a day to the view: watch the railway work its way through an Alpine landscape, then arrive in another country without having spent the journey navigating a road.
The appeal is partly the progression. A photograph can show one bridge or mountain. From the train, the interest is how those scenes connect, and how the surroundings change as the journey continues.
Choose the train as well as the line
Rhaetian Railway describes the Bernina Express route from Chur in Switzerland to Tirano in Italy, passing the Landwasser Viaduct and Bernina Pass. Its panoramic carriages are a defined visitor product, not a name for every train using the railway. Bernina Express
The operator also sells reservations on certain regional Bernina-line trains. That page explicitly says those services are not the Bernina Express and do not have its panoramic carriages or additional onboard services. If your ambition is the Express itself, follow the Express booking route. If your interest is the railway with more freedom to construct a journey, investigate regional connections on their own terms. Regional reservations explained
Neither choice is automatically the more authentic experience. The useful question is whether you want a panoramic journey arranged around a particular service or a day built from individual train legs and stops. Compare the actual timetable, ticket and reservation requirements for the date you intend, rather than assuming a rail pass or a regional reservation covers every version.
Let the crossing have its own day
Consider staying near your departure point the night before. It makes the morning less dependent on a long chain of connections and lets the journey begin before the first photograph-worthy view. At the other end, an overnight stop can turn Tirano into a place you reach rather than a platform you immediately leave.
A same-day return may suit some itineraries, but price it in time as well as money. Repeating a route in the other direction is a different day from crossing once and settling somewhere new. Do not build an evening flight or another critical commitment around an optimistic reading of a train schedule.
Check your selected service for engineering changes and route variations. A famous image associated with the railway does not establish that every departure on every date passes that location. The journey you book should match the journey you hope to take.

Look beyond the camera
Choose the season for the landscape you would enjoy, then accept the weather that comes with it. Clear mountain views cannot be included in a reservation. It is worth wanting the railway experience itself, including the possibility of cloud, rather than purchasing a precise recreation of an advertising photograph.
Keep your belongings manageable and ask the operator about luggage and any boarding assistance you need. Plan food and drinks from the current service information instead of assuming a full dining experience is included.
During the crossing, put the phone down for a while. Watch a scene arrive and disappear without trying to preserve all of it. One or two photographs and a note about the changing landscape may recall the day better than hundreds of similar images through glass.
The milestone is a passage through the Alps, experienced at the pace of the railway. Tirano matters because it gives the journey an ending. What you have made room for is the space between the two stations.