Speaking of overcrowded regional trains: In the past few days, hardly any journey with the 9-euro ticket was comfortable.
While you were thrown out before departure on some regional trains of the Deutsche Bahn because the train was too full, you can even travel in first class with Interrail.
A full first-class pass costs more than 100 euros for 7 days of travel. Our tip: reserve a seat in first class on the train yourself. A reservation is mandatory in some countries anyway, and the difference in price between first and second class is often minimal.
Another advantage of Interrail: Night trains are also included, so you can sleep comfortably on the train and save on hotel costs. This is a real insider tip, because even if the night train arrives the next day, only the day of departure counts as the day of travel.