I'm thinking about doing a half marathon next year in Beijing!? It's part of the Great Wall marathon, I'd just be doing the half. I'm sure that will be challenging enough considering the hills, not to mention the poor air quality. I'll keep you posted as I find out more! The link below shows the information from the 2008 race. 2009 should be posted soon.

"'The Marathon of the Millennium' is now an international event. The course is awesome with 8K on the Great Wall. With the 1800 steps, varying greatly in width and height, the course is run on some steep ascents and descents as well as some very narrow passages on the Great Wall. Participants in the full marathon will conquer this section twice, while the half-marathon and 10K routes will travel through the farmland and villages and cover the 1800 steps of the Wall only once. The longest part of the course is flat with some rolling terrain as well as some dirt road as it travels through the Chinese farmlands and villages."

http://www.kathyloperevents.com/gwm/