Hi,
Thanks for reaching out! Your upcoming trip sounds exciting, and I’m happy to help clarify the visa requirements for your short stay in Beijing.

Since you’re traveling on a USA passport and will be transiting through China, you can take advantage of China’s 240-hour visa-free transit policy (previously 72-hour and 144-hour, now expanded to 240 hours in some regions). This allows you to enter and explore Beijing without a visa for up to six days (240 hours) as long as you meet the following conditions:

Your itinerary must qualify as a transit. This means you must be flying into China from one country (e.g., the USA) and out to a different country (e.g., South Korea)—round-trip flights between just the USA and China do not qualify.
You need a confirmed onward ticket to a third country (South Korea in your case), scheduled to depart within the 240-hour limit.
Your passport must have at least three months of validity remaining at the time of entry.
You must apply for a temporary stay permit upon arrival at Beijing Capital International Airport (PEK) or Daxing International Airport (PKX). This is done at the dedicated "240hour Visa-Free Transit" counter at immigration.
What You Need to Do Upon Arrival in Beijing:
At check-in for your flight to China, inform the airline that you’ll be using the 240-hour visa-free transit and show your confirmed onward flight ticket to South Korea.
Upon arrival in Beijing, go to the Visa-Free Transit desk at immigration and apply for a temporary stay permit—this is a simple process where your passport will be stamped, allowing you to enter China.
Fill out the arrival card, which is available at immigration.
Once through, you’re free to explore Beijing and other approved areas without a visa!

Let me know if you have any other questions, and have a fantastic trip to China and South Korea!