airport layover

The Mutianyu Great Wall is over 60 km (37 miles) from the airport. it could take as long as 4 - 5 hours by public bus. so i suggest that you book a one-day tour to the great wall. It takes 1.5 - 2 hours on the way, and at least 2 - 3 hours to climb the wall. so you need totally 7 hours for this trip. it costs about USD 200 for private tour for one person, the price can be lower if you have more people in your group.
you don't need to pay the visa to leave the airport. but you need to declare to your airlines if you plan to use the 72-hour visa free stay.