The southern of the two great Han-dynasty passes, about 70 km south-west of Dunhuang and rather less impressive than Yumen Pass — what remains is a lonely brick beacon tower on a low hill — but with a freshly built museum and reconstructed gate complex that explain the Silk Road customs system and the military garrison that policed it. The wider site includes a wine bar where you can drink a cup with a recital of the famous Wang Wei poem, which sounds gimmicky but is actually fun.
Often combined with Yumen Pass in a single day, although the two are on different roads and the round-trip from Dunhuang is long. Less atmospheric than Yumen, more accessible and more informative — better if you want context, worse if you want desert silence.