I'd never before heard of the hillclimbing event for motorcycles held at Rachau, Austria, every year from 1995 to 2004. Apparently it was regarded as the toughest hillclimb of them all, bar none.
I found this video of the 1998 Rachau event via an e-mail from Tim G. After viewing it, I can only boggle in amazement. Apparently the object was to ride your bike up the mountainside as far as you could before you fell off. The winner was the person who reached the highest point.
It's now discontinued, so the Rachau Hillclimb is no longer the 'toughest of them all' - but it certainly seems to have been the most insane!