“It was a pure adventure tour,” he said.
Hortlorf and his fourth wife Christine had met in 1989 after Holtorf's placed a personal ad in Die Zeit newspaper following his third divorce.
The two travelled together for 22 years, often accompanied by Christine's son Martin, until Christine died of cancer in 2010. The worldly twosome made their union official two weeks before her death.
But shortly before she died, Holtorf promised her that he would complete the world tour in her memory.
Shooting for the record
Holtorf can't quite remember when the idea hit the pair to travel the entire world, but they knew that they wanted to break into the Guinness Book of Records.
His world maps, which he calls “more important than my passport”, show the routes already travelled, all the countries he's already visited, as well as his future plans.
Their ambition and his sunny personality were what allowed him to get past more than a few uncooperative border guards and police chiefs.
Now the job is done, it's with “a certain melancholy” that he has returned home, Holtorf said.
But he plans to put his mechanical skills to good use restoring old cars.
Holtorf and Christine spent five years criss-crossing Africa, before deciding to make the trip to South America, which he knew well from a stay there earlier in his career and wanted to show his wife.
The two continued on through North America, Asia, Australia and all the countries of Europe.
But places closer to home weren't the main event, Holtorf told Stern.
The plan was always “to travel the world, not Europe, to go where others don't want to.”
In a few countries, Holtorf was the first foreigner allowed to bring in his own car.
He fondly recalls trips like these as “pioneer journeys”. A trip to Myanmar alone was six years in the planning.
A former manager at Lufthansa and South German airline Hapag Lloyd Flug, Holtorf had saved up enough money to begin his trip by 1989.
But he and Christine were avid cartographers, and financed their further travels by creating the first detailed map of the Indonesian capital Jakarta, which they updated constantly from 1977 to 2005 on their regular visits.
The map's latest edition, a 400-page “city atlas” of the city of 30 million people, sold 150,000 copies.
Best-travelled car in the world
Holtorf accomplished the entire trip in his sky-blue 1988 Mercedes 300GD, nicknamed “Otto”, which stood proudly on Berlin's Pariser Platz in front of the Brandenburg gate on Wednesday.
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He kept Otto running with spare parts that he always had on hand and the car rarely broke down, despite being regularly overloaded by 500 kilogrammes.
The air-conditioning system was removed after just two years on the road and given away to a Kenyan mechanic.
“What's not there can't go wrong,” Holtorf said.
Otto is still running on its original engine, although it's experienced some unusual repairs including an axle bearing change 5,000 metres high in the Andes mountains.
Holtorf will hand the key to Otto back to Daimler chairman Dieter Zetsche in a ceremony on October 11.
The actual key is a copy made in Jeddah, Saudi Arabia, as the original has long since worn out.
Otto will stand in the Daimler Museum in Stuttgart as the best-travelled vehicle in the world.