What  is the longest train trip you ever took?

I once had some leave time to kill in the Navy,  so took Amtrak from Seattle   to  NYC.  

That was a damn long trip.   Second longest, was the entire length of Italy,  from Milan, to Palermo. 

train , would be from L.A. to Upstate New.York .Thats not including the flight from melbourne australia to .l.a.  and a train from  L.A. to sycarus , seen alot of america that way .

Rome to Amsterdam.      

The longest rail journey in the world (and getting longer) is the stuff of legend—a train ride that starts in Moscow and ends, more than six days later, in Vladivostok.

Three days. Toronto to Edmonton, and Vancouver to Winnipeg

""The Cardinal" from Washington DC to Chicago.  It would have been on time. but ahead of the train, a car played chicken with a freight train((and lost), and the crossing was closed for 2 hours while the police investigated

((outside of Chicago)_and we pulled into Chicago 2 hrs late.

New Orleans to Yuma.   Not much different from a trip by a small ship

I like to do my own driving. To answer you though, my longest train trip was Oakland to San Francisco and back.

London to Fort William, about 500 miles but takes about 12 hours so the sleepers arrive at the right time. Spends half the night shunting around Glasgow.

Bergen to Oslo in Norway was about 7 hrs for 300 miles and was fantastic, highly recommended.

Boise Idaho to San Diego California...... naval training center... the beginning of four waisted years

Los Angeles, California to Topeka, Kansas.

Was a terrific experience.