I travel by train a lot now, so I use it as an opportunity to get some training done.
Last Thursday I spent a total of 8 hours on buses and trains, plus about 1 hour walking. That must be a PB for most land-based transport in a day.
It is so boring to be stuck on trains, most of all in the evening when it is dark and there is nothing to see out of the window. That's why I do apnea on them. (And sometimes also for the same reason as BennyB

)
Yesterday I did a CO2 table for an hour on the train and I didn't even notice the train journey. I just found myself at my destination.