I have yet to run a marathon but it is definitely a check box on my to do list; a simple city marathon would do but why not strive for something more exotic like running it on ancient wall built over 2000 years ago to protect a country from Mongolian Invaders. Old mis-matched stone, high altitudes, and in a foreign land whats not to like about the idea. Add in getting to explore China's great cities of Bejing and Shangai as a bonus.