I'm traveling to India and Ethiopia soon and have the option to change my flight and have a 12 hour layover in Beijing (arriving at 12 noon and leaving at 12am). I've been to Beijing before but wouldn't mind seeing some sites again. Apparently, I won't need a visa as a US citizen since the trip is less than 72 hours. Which sites can I fit in? There are any special procedures at customs that I need to be aware of before leaving the airport? How easy is it to get into the city from the airport and visit the Forbidden City?