Hello,

My wife and I are flying back from Bangkok to the US via Beijing in January next year. We have a 13 hour layover in Beijing (arrive 0600, depart 2100). Is it possible to clear customs and wander around the city for the day, then come back and continue our flight? Are there any tour-type services that we can book at the airport that make this simple? Thanks! (EDIT: both US citizens, if that matters... understand we'd have to get a visa before we arrive).

Yes, you can do this. No visa needed, you may use Transit Without Visa privileges since your time in transit is under 24 hours. Assuming you are arriving in Terminal 3 (on CA or TG), deplane and follow everybody to the Immigration stations. Look for the one marked "Special" or similar which is usually at the far end of the long row of desks. Have your onward boarding pass (or a printout of your confirmed full itinerary showing the onward flight) ready to show the officer along with your passport. Tell them you want to go into the city to sightsee and shop. They'll stamp you in for TWOV and you're then free to continue through, pass Customs which is no big deal, and exit the terminal and head into the city. Your bags should already be checked through in BKK so no need to deal with in PEK. If you have carry-on luggage that you wish to temporarily be rid of, then put in Left Luggage on the nonsecure side of terminal. (Don't leave valuables though).

You have a nice amount of time to play with. Aim to be back at T3 by 19:45 to allow for getting back through Immigration and Security to airside. I'll assume you'll have your onward boarding pass already.
I suggest you dispense with tour guides and read some other threads on this forum for ideas about what to do in the time you have. Whether to see or defer until the future the Great Wall is the first decision to make, as that sets up the parameters of the visit.

There are 20+ threads on this topic.

Check recommended drivers thread - depending on what you want to do (e.g. Great Wall) it may make sense to hire driver in advance for airport pickup, and take you to Great Wall and then back into city for something else--they could drop you at Summer Palace or Tianenmen Square, from which you could see more of city and take taxi back to airport.

depending on when you get in, it takes a good hour to get downtown.