How can I get to Yanmenguan Pass from Datong?

First, you need to take a long-distance bus to Dai County, then hire a taxi to the Yanmenguan Pass.
But if you will also visit other places in Datong like the Mt. Hengshan, the Hanging Monastery, etc, the best way is hiring a car and local driver, about rmb350-400 per day. It will save you time and energy.