Huanghua Cheng Great Wall ride
I've done this a dozen times, at least. This is the route Aaron and I have done for 5 years, going out, staying overnight at the base of the wall, and coming back the next day - and Hua Lin has done it the last 2 years as well.
The first 20k are flat, boring, and not so pleasant with city traffic, but after crossing the road at Xiaotangshan it gets better, and once the mountains start in Xingshou it is pretty good. The mountains start with about 15k basically up, though with breaks and never too steep, up to the top of the mountain at Huanghua zhen, when there is a great 5k downhill, after which there is what seems an interminable 10k when you think you should be done, but aren't. And then finally over the last crest, down a short hill and a left turn to the bridge, and you are there.
The restaurant we have gone to for over 10 years is the last one on the right with the balcony on the roof - there is another one which looks just the same just before it, but it isn't as good. We originally stayed in one across the street because they had private bathrooms, but now stay either in the wooden huts down next to the wall or at the same place we eat.
Since 50k isn't really a good workout, usually the second day I get up early and bike out to Sihai , a round trip of about 50k, but with a nasty hill on it.
View from the first crest of the wall: the restaurant we always eat at is the white rectangle at bottom center