Yes. It's unbelievable but true. Some people pay money to sit beside airport runways noting down serial numbers on planes and call it a holiday. The detention of 12 British plane spotters in Greece - mistaken for spies - highlights once again to the world this oddball obsession.

But is it such a funny preoccupation? Aren't the majority of things British people do on holiday odd? Like peeling off our clothes to reveal pink skin and sizzling like bacon in the sun for two weeks? Or even more bizarre, flying halfway across the world to lie for two weeks beside a hotel pool and not even getting as far as the beach? Believe it or not, plane spotting is, for some addicts a form of stress relief. When I was at university there was a student who would nip down to Manchester Airport whenever he couldn't sleep or was suffering from exam nerves. He'd stand on the airport roof watching the planes take off and land and return feeling calmed.

I remember a holiday company that received 1,000 phone calls in response to an article about stressed-out executives going to the north of England to learn dry stone walling. The usual response to a travel article is about 50 phone calls, so that was an unusually popular response. There's something terribly satisfying about seeing a list of numbers filled up in a notebook, or completing a wall, or even seeing those tan lines develop. It's all the same sort of thing really. Bizarre forms of pointless fulfilment.

Other people's ideas of a good holiday never cease to amaze. Who are these people who go on cornfield tours of the US, sitting in coaches for hours on end, day after day, looking at cornfields go by? Or people who travel to Delhi to train spot rather than hanging around King's Cross. Or hanging around Monaco noting down details of boats in the harbour? Or going to take pictures of racing cars? This week, I have been phoned, faxed and phoned again by a company organising short breaks to British horse racecourses. Racecourses? There's obviously a market (www.discover-racing.com if you're keen).

One of the best places to look for a special-interest holiday is in the Association of Independent Tour Operators brochure (0870 751 8080). Fishing, butterfly tours, Dutch bulbfield tours, bridge get-togethers and orchid hunts are all on offer.

But the prize for the most nerdy holiday of the year has to go to a colleague who spent this summer trailing Neil Young around Europe on tour. He attended gigs in Sheffield, Birmingham, La Coruña and Porto, before going home again for a week and flying to Rotterdam a week later. If there were any variations in the set, the journalist in question filed copy to the Neil Young website to report. Call that a holiday?

· Do you have examples of holidays more nerdy than these? Please share: Jeannette.Hyde@observer.co.uk