This summer I took the ferry from Hirtshals, Denmark to Seydisfjordur, Iceland. 2 full days, over 48 hours of travel time. And back.
Relatives and friends thought my wife and I were crazy - or at least eccentric. Why would you waste 4 full days (+ 2 days to get to and from Denmark by car).
Turns out, travel time is still travel. And what a beautiful time that was!
There is no stable Internet conncetion on the ferry itself (no cell connection AT ALL at sea), plus you have to pay for it a pretty hefty fee. So from observing other people, +95% did not have Internet access at all.
The ferry itself is not huge, it is not a cruise ship. But large enough to be entertaining and fun to explore. Kids had a few attractions, including a tiny cinema. They sold popcorn though, that's all kids cared about besides the Minecraft movie.
For us, adults, there were a few bars, restaurants to hang out. Even a little library, a corner with board games, couple shops.
Because people were not glued to their phones, you could actually meet and talk to other people, have non-trivial conversations. People would read books, have a sip of coffee, walk around.
Not once did I get bored, not once did I not know what to do. Sure enough, I would pull out the iPhone from my pocket only to see it is completely offline. What was also fun: if I went out with the kids, there was no way I could let me wife know we would be late or any other matters. Same the other way.
Life felt slower, but somehow more real?
Anyway, I can only recommend a travel experience like this, at least once in your lifetime. For us, it became part of the memories we made, besides visiting Iceland itself. I can imagine the same being the case if you travel long distances by train.