Climbed L'Alpe D'Huez back in the summer of 2007.
I had only bought a road bike about a month before, didn't own any cycling clothing (don't know how I went 15 years without realizing the benefits!). I was about 1.5 months into doing more than just riding casually on a weeknight and weekend and actually 'training'. If you could call it that. So I was in descent shape, but nothing spectacular.
Clocked time was 1:22 up.
This is a picture from the first 4 km, which were brutal. It actually looks steep in the picture! About 10% over this section, but once you get past this, the rest settles into a nice 6-7%, which as far as I'm concerned is fairly easy to spin with the proper gearing. Huez is also one of the steeper climbs, most others were not as bad. I personally don't mind climbing, so I'm biased, but I didn't find it overall that tough! Then again, selective memory might be setting in right now. But really, with some determination they are all possible.
The thing that made it easier to make it up was all the other people around. All shapes and forms. I still remember a young woman who did not appear to be in great shape and she was rather large. She was on a mountain bike probably running 20x34. She couldn't have been going more than 4 km/hr and I could tell she was suffering. But you could tell she wanted to make it. When I passed her, my pain, suffering and sense of accomplishment seemed pretty insignificant.
Mountain Moo's at the top of Huez.
Drove Galibier (and others).
We stayed at a B&B up the Col de la Croix de Fer. They had the best dinners. It catered to cyclists and motorcyclists. Every evening the dinner table was filled with lots of dutch, german and belgian cyclists, all discussing the climbs. The various home made Eau de Vie with all sorts of flavouring was awesome after the meals.
There is a group of dutch guys who still don't believe I made it up in that time. I don't blame them considering I was renting a bike and what I was wearing. I doubt the people I rented the bike from believed I made it either when I returned it 2 hours later. Likely figured I gave up at about 4 km.
In the works to return in the near future and do a lot more riding.