Long before WOW and Norwegian Air had $99 airfares luring young people across the pond, there was Eurail, the post-World-War-II, trans-European train network that offered dirt cheap, all-you-can-ride passes for intrepid Americans looking to explore a region just recovering from the most destructive war in history.
What resulted was the first iteration of the Euro-trip, a rite-of-passage trip for young adults in the summers between college spent riding the rails in a place that, at the time, cost a fraction of what things did at home. If you wanna learn what it was like, ask a Baby Boomer.