As students, we were on our way back from Sweden in my first car - a purple (!) Triumph Herald - and suddenly decided to turn left and have a look at Berlin.
Until then, I hadn't realised that Berlin was marooned in the middle of East Germany, and certainly wasn't expecting that I was about to draw back from the brink of far-left politics, let alone start to understnd what the cold war was all about.
The cost of driving through East Germany
In those days, a green insurance card coveered you to drive all over Europe - except for the DDR. Communists they may have been, but they knew how to make a quick buck or two. At the border, you not only had to buy their insurance to drive along their autobahns, but you also had to buy a visa.
Once on the way, it became clear that the East Germans had done no repairs to the autobahn since before the war, presumably to make it as difficult as possible to drive to West Berlin. There were pot-holes everywhere and it was impossible to go much more than 30 mph - which was slow even by Triumph Herald standards.
Mirrors on sticks
Getting into West Berlin meant waiting a very long time for the privilege. One set of border guards scrutinised your passport and newly acquired visa with a degree of bureaucratic assiduousness that made you wonder what unspeakable things they'd been up to during the war.
Then more guards appeared to make you unpack everything and take out the back seats of the car. Not content with finding no escapees hiding there, they produced long sticks with mirrors stuck on the end of them to poke under the car. Triumph Herald's may have been famous for having a proper chassis, but even I knew that there wasn't room to hide a body, dead or alive, underneath it.
Once this ridiculous process had been completed, we were allowed to drive through the high barbed wire fences into West Berlin.
The unexpected road block
Although we had a map, we'd no idea where to go, let alone where we were going to stay the night. So we started driving about until the road ahead was suddenly blocked. It wasn't just that there was a wall across the middle of it, but soldiers with guns also appeared as we approached.
I've no idea what the West Berlin laws had to say about doing sudden U-turns in the middle of a street, but there was no choice - and the Triumph Herald was also well-known for its unusually sharp lock that enabled you to tuen front wheels to almost 90 degrees).
An uncomfortable night and a hasty retreat
Having had to spend so much buying a DDR visa and DDR car insurance, we were so short of cash that we had little choice to sleep in the car. Nor, given that this was long before reclining seats had been invented, did we get much sleep at all.
By dawn, we agreed that we'd had enough of Berlin and it was time to go home. Knowing that no one would be mad enough to try to escape from the West into East Germany, these border guards didn't bother with mirrors and weren't very interested in our passports or visas.
Over the border to freedom
But when it came to getting across the border from East to West Germany, out came the mirrors on sticks again. And, early though it still was, we had to wait in a traffic jam for an hour or two before being allowed out.
At some stage, we must have bought some bread, cheese and a few bottles of beer, because my most vivid memory of the trip was having a picnic on a hill at the edge of a wood somewhere near Magdeburg.
We didn't say much. Left-wing students of the sixties we may have been before the previous day, the only thought going through my mind was: "For the first time, we now know know what freedom really means."