When we are allowed out into more European countries again, this is an option for holidays.
(This applies to walking trips as well, really, of course.)
This was an interesting and well written article about travelling by train for climbing trips in Europe. Train travel can be enjoyable in itself, there's things to see out of the windows to give us ideas for future trips.
https://www.ukclimbing.com/articles/destinations/a_guide_to_climbing_trips_...
The Seat61 website shows how train journeys (e.g. from London into Europe) can have 75 to 90% lower CO2 emissions than the same journey by plane.
https://www.seat61.com/CO2flights.htm
An article on train times and costs:
https://www.dw.com/en/trains-vs-planes-whats-the-real-cost-of-travel/a-4520...