It was a free afternoon in Munich that inspired John Graham-Cumming to begin compiling the Geek Atlas, a guide to the top sites to see when technology enthusiasts turn tourist.
While looking for somewhere to kill a few hours, he discovered Munich's Deutsches Museum. It's one of the world's biggest science museums and the very fact that he hadn't heard of it before drove him to wonder about similar places of interest in other countries.
"I went online looking for a Lonely Planet guide for scientists, and I couldn't find one," says the self-confessed mathematics lover.
"I called a few tourist boards and asked about scientific attractions. I realised I could get a short list of really mainstream ones but there seemed to be a gap in the market for anything more detailed."
The main criteria for inclusion in the resulting atlas were that each attraction had to be open, interesting and accessible to English speakers.
Mr Graham-Cumming deliberately chose to leave out sites connected with US space agency Nasa.
"There are only so many Nasa sites this book could hold," he says.
Of the 128 places featured in the book, 12 are in France, 45 are in the UK and 46 are in the US. He admits the ones he chose are more a reflection of his own travels than a comprehensive global guide.
Given the nature of the book's title and those it is most likely to appeal to, it is not surprising to find that the locations of John Graham-Cumming's suggestions are provided in geographical co-ordinates rather than addresses.
51° 19' 51.6" N, 0° 3' 9.5" E, for example, will get you to Charles Darwin's former home, Down House - but don't bother looking for the postcode.
"It's hard to pick a favourite place," he admits. "The first time I saw Charles Babbage's Difference Engine No 2 reconstruction in the Science Museum I shed a tear."
The 19th Century scientist is now widely regarded as a computer pioneer, particularly for the work he did on the Analytic Engine - the successor to the machine that moved Mr Graham-Cumming to tears.
He also enjoyed the National Cryptologic Museum in Maryland. "It's the only place in the world where you can walk up to a Nazi Enigma machine and type on it," he explains. "It's thrilling - if you're a geek."
The Hunterian Museum, home of the Royal College of Surgeons' fascinating if macabre anatomical collection, is another popular haunt.
"It would be an interesting place to come on a date," Mr Graham-Cumming said. "You'd certainly find out quite quickly whether you were suited..."
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