To enter the contest, which includes round-trip airfare for you and a guest from anywhere in the world, all you need to do is head to the official Great Wall listing and respond to the following prompt by the August 11 deadline: Why is it more important now than ever to break down barriers between cultures? How would you want to build new connections? Winners will be selected on August 13 and notified via Airbnb within 24 hours.
To win, you'll also need to be available to travel to Beijing between September 3-9, and your Airbnb account needs to be in good standing (hopefully, you didn't trash your last host's place).
If you don't manage to score a stay at the Wall, you'll have other opportunities to crash in an especially cool spot on Airbnb's dime in the future. The company has hosted a number of special "Night Of" one-off stays in pretty spectacular locales like the Catacombs of Paris and the Guinness Storehouse.
UPDATE 8/8: Airbnb called off the competition after it received mixed reactions on Chinese social media, with some arguing that allowing people to stay on the Great Wall overnight not only exploits its historic significance for PR purposes, but may contribute to its degradation. In a statement posted online announcing the cancellation, Airbnb said that it "deeply respect[s] the feedback" and "made the decision to not move forward with this event."