Specifically one with an on-board spa and enough wine to keep you sated for the duration of your stay.
Our candidate: The Indian Maharaja, a new private luxury railcar offering cinematically lavish tours of northern India starting this Wednesday.
It's everything you're used to from continental hotels, but dropped on rails and set loose on the subcontinent. That means you'll be able to take in a steam bath, get a quick rubdown courtesy of the onboard masseuse, or (in case of emergency) send a few emails without stepping off the train.
And, more importantly, you'll be bedding down in a bona fide hotel room instead of a sleeper car, decked out with a full bed, a minibar and a butler to bring you whatever you can't find in the room. The only difference from your usual home-away-from-home will be the unpredictable vista out the window—which should vary between red sandstone ghost towns, 10th century fortresses and some unusually friendly tigers, courtesy of Ranthambore National Park.
Of course, not everything's railroad adjacent, so you'll also take daytrips to exotic locations along the way, including one that lets you tackle the countryside while riding an elephant.