These tombs date from approximately AD 220–420 (the Wei and Western Jin periods) and contain extraordinarily fresh brick-wall paintings (some sadly ineptly retouched) depicting scenes of everyday life, from making tea to picking mulberries for silk production. There are thousands of tombs in the desert 20km east of Jiayuguan, but only one is currently open to visitors, that of a husband and wife. There is a small museum that's also worth a look; it's the only area where photos are permitted.
A taxi here from central Jiayuguan will cost around ¥70. If you pay a little more (¥100), the driver will also take you to nearby Yemawan Cun (野麻湾村, Yěmáwān Cūn), the crumbling remains of a former walled village about 10km from the tombs.