Thank you so much for your great additional tips @sacrezm! True, skyscanner is another very useful website. I'm just a bit disappointed about skyscanner as it sometimes shows prices on the first page, which are not true at the end. With kayak or kiwi, i didn't have this experience yet. Interrail is also a great way to explore Europe. Just the ticket prices were quite rising in recent years so depending on which countries you wanna go and how much you wanna travel, single tickets might be even cheaper at the end. About hitchhiking: In my experience, it can be useful sometimes to write where you wanna go, but the best experience i had was asking people directly at gas stations where they go and if they wanna give me a lift. I will definitely consider your "Secret tip" for my next travel!!;-)