If you are traveling in Europe by train, there are a variety of passes from which you can choose.
Most rail lines offer national passes for travel within one country.
There are reasonably priced tickets for those wanting to travel from one country to another country. Also, you can choose a Europass or Eurail Pass, which give you more flexibility on where and when you travel. You determine the number of travel days and countries visited. They don't, however, extend the number of days on your pass. Even if you are just passing through a country, you must have that zone on your pass or the conductor will charge you an additional fee.