The trick to get an flexible affordable ticket between European cities is to know that interrail tickets(https://www.interrail.eu) is no longer limited to youngsters on a multiweek backpacking journey.

Back when we were still allowed to travel i spend a fair bit of time traveling between non-airport cities which meant that an 8-10 hour cross border train ride was often the only alternative to even more time spend waiting at airports, which still required muiti-hour train journeys to the final destination, and i really did enjoy that mode of transport, but it does take some mental adjustments as delays are pretty common on the railways so if you have a "must meet" every connection as scheduled schedule where you cannot just jump on the next train out things will get messy.