Train journeys that are the destination

Glacier Express

Zermatt to St. Moritz, Switzerland en.wikipedia.org

Your Swiss Travel Pass covers it, just pay the seat reservation.

West Highland Line

Glasgow to Mallaig, Scotland en.wikipedia.org

Sit on the left heading north for the viaduct.

Trans-Siberian Railway

Moscow to Vladivostok, Russia en.wikipedia.org

California Zephyr

Chicago to Emeryville, USA en.wikipedia.org

Qinghai–Tibet railway

Xining to Lhasa, China en.wikipedia.org

Oxygen is piped into the carriages. You'll still feel it.

Bernina Express

Chur to Tirano, Switzerland/Italy en.wikipedia.org

Flåm Line

Myrdal to Flåm, Norway en.wikipedia.org

Settle–Carlisle line

Yorkshire and Cumbria, England en.wikipedia.org

Ribblehead Viaduct is the highlight. Get off at Dent to walk.

Semmering railway

Lower Austria, Austria en.wikipedia.org