InterRail
An Inter Rail pass is a train ticket lasting for a certain amount of time that allows unlimited train access on many European and adjacent rail lines.
The program started in 1972, and was initially limited to travelers 21 or younger. The 21 initial countries were Austria, Belgium, Denmark, Finland, France, West Germany and East Germany, Greece, Hungary, Ireland, Italy, Luxembourg, the Netherlands, Norway, Poland, Portugal, Spain, Sweden, Switzerland, the United Kingdom, and Yugoslavia. Turkey and Morocco are now also part of the program. Since the fall of the Iron Curtain, Poland, the Czech Republic, Slovakia, Croatia, Macedonia, Serbia, Slovenia, Bulgaria, Romania and northern Morocco have joined the program; leaving only Bosnia, Albania and the UK not yet to join it.
Starting in 1998, Inter Rail passes became available to all ages, but there are currently three age-based pricing levels, with children under 12 paying the least, and adults 26 and over, the most. The service area has been divided into eight zones; the cheapest pass is limited to within a single zone--the most expensive allows travel to any zone(s). In between there is also a two-zone pass available.