In the years following World War II and up until 1989, Germany was a divided country, and its capital city of Berlin lay right on the border, in fact, the border bisected it.
There was a wall -- the Berlin Wall, which came down 30 years ago, effectively ending the Cold War -- separating the more liberal, Westernized West side of the city -- controlled by the Western Allies after World War 2. East Berlin was given to the Soviets after WW2 and was transformed into the German Democratic Republic (GDR), a repressive police state controlled by the Soviet Union.
Many people who lived under the GDR sought to escape to Western Germany but weren't allowed to do so. As a result, many attempted to cross the border illegally, which could mean that they'd be shot (it's at least 327 people were) or at the very least, imprisoned if they were caught.
The border, while heavily guarded and regulated, wasn't completely closed. West German citizens were regularly allowed to cross for business purposes or to visit family. This gave some enterprising Germans a means to help others escape the GDR.
In 1963, a man named Klaus-Günter Jacobi decided to help his best friend escape East Berlin and before being forced to report for duty in the East German army. To do so, he decided to modify his BMW Isetta to be able to hide a body.
Now, if you're not especially familiar with the Isetta, it's a tiny bubble car with a motorcycle engine at the back and barely enough room for two people to sit in the bench seat behind the front opening door. Space is at a premium, but Jacobi -- who had trained as a mechanic -- found that there was a dead space behind his seat and next to the Isetta's tiny engine that could be used to smuggle a person.
He modified his car and crossed into East Berlin one night, picked up his friend and set about making the crossing back into West Germany. He made it through the border, and his idea -- the modified Isetta -- was used to eventually smuggle nine other East Berliners to the West.