Originally Posted by
mnredfox
I have not done this recently, but a friend who lives in Dali recently took the train from Beijing to the wall and said it was a great experience and worked really really well.
The train would be to Badaling GW--not a recommended part when there are plausible alternatives, and it takes too long. With only one useable day, this OP doesn't have that kind of time to waste if he wants to see something in the city as well. And yes, as above poster says, there is a gauntlet walk from station to Wall itself. Stick with Mutianyu and car.