Hiya, this was pre-pandemic but me, my partner and then 11-year-old went interrailing and spent some time in beautiful Brac in Croatia and also stopped at various places to see friends.
the train tickets weren’t madly expensive, my partner was 60 so his was cheaper, hers was a child. We were really excited about the couple of sleepers but actually they were pretty uncomfortable and it was lucky that the athletic kid was there to scramble to the top bunk. They were three berths but I think only quite a fit person could manage the top.
we went from London to Paris to Lausanne in Switzerland (to see friends), to the Italian lakes, to Milan then to the coast and caught ferry to Croatia, spent a few days on beach, then Budapest (to see friends) then Berlin, Amsterdam, spent a few days at Efteling theme park, Brussels and home!
look into Interrailing tickets, you can plan your own route! We were going for the month, guess it might not be worth it for a shorter time. Good luck!