My visit to Beijing was part of my Japan->UK overland trip. I had a few nights there, so I spent a day in the centre of Beijing looking around the Forbidden City, and Tiananmen Square.
The Forbidden City is an interesting area, but the best place to view it is the hill in Jingshan Park, that way you can see all the teracotta roofs of the city, and imagine that only a few hundred years ago the whole of Beijing looked just the same.
I decided to go to a part of the Great Wall that has fewer tourists as it's a bit further away from Beijing. The drive to Simatai took about two hours. Then I took the cable car half way up to the wall. After that the climb got a bit tougher, but that didn't discourage the old ladies selling tourist rubbish, they seemed to be able to keep up with me no matter how fast I moved. In end the end I just stopped and just kept saying "no" until they gave up.
I'd seen many pictures of the Wall, but none of them do it justice - you really can't comprehend the scale of the thing until you actually see it. It truly is a wonder of the world!
I found myself in Beijing at the start of my 'Silk Road' tour in 2008, and although I didn't have much time in the city I did make it out to the Summer Palace gardens, where there is an amazing 'boat' made out of marble. Well, it's the size and shape of a boat, but it's a folly, as it doesn't move. The royal family used to take afternoon tea there. It's also not made out of Marble, but wood painted to look like marble.