Excellent joint for Tibetan eats, and always busy with locals, even if it is somewhat lacking in atmosphere. The house speciality is yak meat hotpot, and they do a small version for two people (¥80), but the mómo (馍馍, Tibetan dumplings), which come in meat or veggie versions, and the spicy yak-meat pizza are good alternatives.
To find it, walk west of the big square underneath Guishan Temple, turn right on the first street you come to and it's about 100m ahead on the left-hand side.