Recommendations for layover visits from Beijing airport?

Hello everyone!

I will soon have a flight that has layovers (both ways) in Beijing airport (PEK). One of them is from 10:50am until 20:00 (so around 9 hours) and the other is from 4:50am until 1:55am (so around 21 and a halg hours).

Any recommendations on what I could do in those hours? I heard that it's possible to do organised layover tours from/to the airport, and wondering if it's better to plan on my own, or those are good. If so, any recommendations of tours or agencies are welcome too.

Thank you in advance!