The Huang Hua section of the Great Wall is about two and a half hours away from the center of Beijing via public bus to Huairou, then a middle-sized bus or taxi to Huang Hua. It's an unrestored section, not renovated like Badaling and Mutianyu, the major tourist sections of the wall. There are two directions you can go hiking on the wall, west towards Zhuangdaokou or east towards the direction of Simatai. The eastern direction was off-limits since workers are in the process of restoring it. The western direction was just starting to be renovated. On the western side, they had done about 200 feet of renovation, and after that it was still natural with no restoration. I takes about 2 hours to walk at a leisurely pace about a mile to a path where you can walk down to a village and get back to the small town there for transportation. I didn't encounter any other tourists on the wall during the entire time I hiked that distance, which is a difficult thing to do in Beijing.This page
describes someone's trip in the eastern direction when it was still open. From what I saw, the western direction is more interesting anyway. This other page
is from someone that went in the winter. Perhaps the hiking would be easier in the winter since there would be less overgrown weeds and bushes in the way.
Given the great speed with which they do construction work in China, they'll probably have renovated much of this section of the Great Wall within the next year, after which I predict it will be crawling with busloads of tourists and lose its appeal. I'd recommend checking it out before then.
The path atop the wall is overgrown with sharp, scratchy waist- and chest-high weeds and bushes, and there's a fair amount of uphill hiking. I would recommend not doing this hike alone, since you could slip and fall off the side and no one will be around to cart you off to the doctor's.
Looking east over a crumbling watchtower towards a reservoir
Inside one of the watchtowers. Some adventerous folks are keen on camping out there overnight. Before attempting, please watch this movie
Looking down on the top of a watchtower