Where exactly is the bus Mi 25 stop located in Gubeikou and how to hop onto the bus to Miyun?

You are adviced to take Bus Mi 25 at Great Wall Bus Stop, which is near the entrance to the Hexi Village at the foot of the Wall. Walk through the village and you will find Wohushan GW.
You may still walk to the the bus stop and take bus Mi 25 across the road to get back to Miyun.
Just a hint: the return bus will stop operating after 17:30. Make sure you get to the bus station on time.