Gansu Province, 665km (412 miles) W of Xi'an, 514km (319 miles) SW of Yinchuan
This was once the point where the Silk Routes crossed the Yellow River; however, whatever charms the old town possessed were buried long ago. In 1998, Lanzhou won the title of the planet's most polluted city by a considerable margin (Chinese towns filled 7 of the top 10 places). This dubious distinction led to numerous and humorous attempts to rectify the problem -- one entrepreneur got backing for a scheme to knock a hole in the surrounding mountains to "open the window" on Lanzhou's smog.
While the smog remains, Lanzhou today is a wealthy, bustling modern city and aesthetic improvements are continually being made; recently the riverside area has been converted into a large park which makes a pleasant place for a stroll. However, Lanzhou still offers few reasons to linger. The museum is worth a look, and the town is a comfortable base for trips south to Bingling Si, Xia He, and Langmu Si (if the latter two remain open to foreigners). But your first action should be to book a ticket out of town.