Imagine this: you queue for a roller coaster, only to find that at the boarding platform there're two cars to choose from. You pick your car, and then are sent haring round a wooden track, fearing for you safety and sanity, racing the other car, the one you didn't pick.
You pass through 'Canal Turn' and 'Beecher's Brook' and other turns and jumps from the famous race at Aintree race course, before bulleting towards the 'Finishing Post', milimetres, or so it seems, ahead (or behind) the other car. And you're on the other side from where you started.
The Grand National, fashioned after the race course, is one of only a few 'Mobius Strip' roller coasters: what looks like two tracks, is, in fact, only one - with a cross over, sort of, midway. It's at Blackpool Pleasure Beach in Lancashire, UK, and is utterly brilliant, if slightly scary (not for speed or anything so easy - but just 'cos it's wooden, and, so it seems, liable to come to bits).
I've tried experimenting to see which car wins, but it's different every time. I guess the only way to really guarantee being on the winning side is, whilst you're in the queue, to bribe all the fat (or more amply proportioned, I guess) riders to get on the car with you. The winch will always wind at the same speed - but you'll gather much more momentum on the way round.
It's an excellent ride.