Here's one of the Kemmelberg:
Okay, it isn't
really the Kemmelberg but it gives you an idea of what it would have been like coming down it before they put the tarmac descent in this year - madness!
I've posted this picture before - it is
The Buttress in Hebden Bridge. I tried riding down it once but only got about 50 metres before I chickened out and that wasn't on the steepest section. I almost crashed when I braked. Believe it or not - this is on the official route of the Pennine Cycleway - crazy decision of the route planners. There is a quiet road parallel to that which is (just) rideable so I think they should have used that instead.
I've only heard of one guy managing to ride up it. I'm going to have a go when I've lost a lot of weight. It wouldn't be quite so bad on a mountain bike, but it would be an absolute killer on a road bike. The bottom section is close to 30% and there is a drainage channel to get over at the top of that.