Question: do i need a passport to travel by train in europe?
Answer: Rule #2: No matter where you're from and even if you don't need a Visa, you cannot spend more than 90 days within 180 days in Europe as a tourist (so 3 months within half year period)! Rule #3: When boarding a train (or bus or plane) in Europe, always have your passport with you, not just a regular ID.