Inspired by this thread, naturally.
Last year, I rode the train from Los Angeles to Chicago, a trip that took roughly 45 hours. Prior to that, I’d once taken the train from St. Louis to Los Angeles. I don’t remember exactly how long that took, but “too long” definitely fit the bill, particularly sitting in the regular seating.
What about you?
Only about 12 hours, IIRC. Most of my train trips were 6 hours or more.
4 days. Emeryville, CA to NYC in coach.
It was a blast!
In 1969 I rode the Great Northern from Chicago to Seattle, and then I think I had to transfer to some other line to get to Portland. Two nights, if I recall correctly. I had one of those little roomettes where the bed was 3 inches too short.
I also tried, a few years ago, an overnight on the Coast Starlighter from San Francisco to Salem, OR. Coach only, without a bed. My seat was very uncomfortable, i would not do that again. However, I had the treat (when I tried to sack out on some bench seats in the snacks area) of hearing a couple of young people in flagrante delicto in a bathroom. I had to move away, they were disturbing my sleep.
Roddy
couple hours; commuter rail from Ueno to Iwaki.
Saskatoon to Vancouver. I was a little kid, so I don’t remember too much about it.
13 hours on the Amtrak train, Montreal to NYC. (Basically an entire day.) Then the same trip back.
The way there was nice. the way back there were 2 noisy, whiny kids behind me.
In general, though, it was good. 
When I was in grad school I used to take the Lake Shore Limited between Toledo and Boston a few times a year. About 18 hours one way. Don’t know what it’s like now, but it was OK back then… a red-eye, not crowded, old cars with bench-style seats you could lie down on, spacious restrooms, and a real dining car.
2 1/2 days.
Moscow, Russia to Tashkent, Uzbekistan.
AMTRAK. Chicago to New York. 24 hours. Coach. Long delays. They ran out of food and drink and water for the toilet. Kinda like a cruise.
Two long-distance train trips - northern Indiana to San Antonio TX in 1991 ( 2 1/2 days IIRC) - travelling coach as a poor college student. Then a half-day by bus to the Texas/Mexico border and another half-day-ish to Monterrey Mexico, where I attended a 6-week “study abroad” program & did the return trip. It was quite the experience, but don’t know if I could/would do it again.
Anaheim CA to west-central Indiana this past summer - 5pm Thursday to 10 pm Saturday - again, about 2 1/2 days - this time in a roomette with my husband (and about 150 Boy Scouts elsewhere in the train!) Having the separate room made the trip more enjoyable - tho I think I’d travel at a different time of year across the Southwest Desert.
Amtrak from Seattle to MSP. Also Portland to MSP. Both about 40+ hours because of bad track and delays.
1977, also LA to Chicago, but more than 48 hours since we ran into snow in Kansas and were hours late getting into Chicago. I was in a sleeper car - several compartments in my car’s toilets froze. We of course ran out of food. And they froze my hamster solid.
I then got on another train from Chicago to Champaign, but I don’t know if that time gets added to the other trip or not.
It was not all bad. This led directly to me getting married.
When my husband was stationed in Spain, and he was on temporary duty in another country, I’d often wander down to the train station, pick an interesting sounding destination, and take day trips. They were only day trips, so I never spent more than about four hours each way on a train on any one trip, but I did spend a lot of time in trains. That’s one thing about Spain that I really miss. I think that train travel is far more comfortable than bus travel. When I traveled by bus, I always got sick from the fumes. And the bus was usually almost as costly as flying!
Glasgow to London, after a redeye flight from the US and a drinking binge.
I was on that train for about 3 weeks. That’s what it felt like, anyway … .
Surely you don’t intend to leave us hanging, do you?
As a kid (too young to remember) I travelled from California to Oklahoma.
Last year, Amtrak, Atlanta to New Orleans and Atlanta to Washington DC. both of those are about 12 hours.
Winnipeg to Toronto, about 36 hours.
Not very long, about five hours from Trento to Munich.
Not all that long. Several trips in the 60s from San Bernardino, CA to Lubbock, TX, and one time when I couldn’t be arsed to find a hotel room and spent the night sleeping on the slow train from London to Manchester and back.