The distance will never differ. A marathon will always be 26.2 miles or 26 miles 385 yards or 42 kilometres 195 metres.
However you want to express it, it amounts to the same.
But the one great variable (well, aside from your present state of fitness) is the route that it takes you on, and here you get the great gulf.
Some marathons are absolute stinkers, some are somewhere in between, some are 26.2 miles of bliss.
My 26th marathon will be the Tokyo Marathon on February 26, and I confidently expect it to be very firmly in that last, much cherished category.
My marathon low points have included Amsterdam and Dublin, both races which get you off to a reasonably enjoyable start and get you over the line with a tolerable sense of occasion.
But in between – and much more so in Dublin than Amsterdam – you get 24 miles of tedium. Berlin wasn’t that much better in that respect.
Dublin was a day of torrential rain, which didn’t help. The cascading torrents reduced everything to an eye-stinging blur as you passed through endless nondescript suburbia.
In Amsterdam, they showed us a few canals and allowed us five or six miles of riverside running. Otherwise, it was deeply-dull industrial estates, dual carriageways and roundabouts.
Berlin was simply big city, vast, sprawling and successive boulevards indistinguishable from the last.
Against that, you have the spine-tingling highs – New York and Paris.
A November marathon, the New York City finishes with three miles in the gloriously-autumnal colours of Central Park after a race which takes you through all five boroughs – as I describe in my new book, Keep On Running (published by Summersdale of Chichester on April 2, http://www.summersdale.com/book/2/569/keep-on-running/)
Paris is similarly generous with its sights – a start and an end at the Arc de Triomphe, an opening stretch along the Rue de Rivoli, a gorgeous five or six miles of forest-running in the Bois de Vincennes and a second half which keeps you close to the Seine for much of it.
The value of a decent course simply cannot be overstated: you need something to lift your soul when the body starts to flag. Stimulate the senses and you push further and further back the moment that tiredness truly starts to kick in.
And that’s why I can hardly wait to get on that start line in Tokyo.
Last October, as part of a group of international journalists, I visited the course on a trip organised by the Tokyo Marathon Foundation with the aim of promoting the event worldwide.
My huge good fortune, just before Christmas, was to be invited back to run it.
You never want to run a marathon without knowing just a little bit about the course. As I stand at the start in Tokyo, I will have it fresh in mind – a mouth-watering route which kicks off outside the Tokyo Metropolitan Government Building before snaking through the hugely-colourful night club district (and no, at nine in the morning, I won’t be stopping off).
Along the way, it also skirts the Imperial Palace and passes through Tokyo’s high-end shopping district before going deep into the heart of ancient Tokyo before a lovely-looking finish at the massive exhibition centre.
Usually, I run to thudding rock rhythms on my MP3 player. There won’t be any need to in Japan. All along the route there will bands and musicians and dancers adding terrific colour and occasion to the proceedings, precisely the kind of boost tired runners need more and more of as they head towards the finish.
Nearly a year after the devastating tsunami, Tokyo is going to be pulling out all the stops to show us just what a vibrant, exciting, indeed thrilling place it is. Few things make me emotional. Marathons most certainly do.
I’ve just completed an eight-mile training run at -8 degrees C through the country lanes of rural Hampshire. I didn’t feel the cold at all. The thought of Tokyo is already warming me up nicely…
Follow me on @marathon_addict on Twitter and on https://marathonaddictuk.wordpress.com/. And have a look at my book Keep On Running (http://www.summersdale.com/book/2/569/keep-on-running/)