Not to be confused with the small Wat U Mong in the old city, this historic forest wát is famed for its sylvan setting and its ancient chedi, which rises above a brick platform wormholed with passageways, built around 1380 for the 'mad' monk Thera Jan. As you wander the arched tunnels, you can see traces of the original murals and several venerated Buddha images. The scrub forest around the platform is scattered with centuries' worth of broken Buddha images.
The attendant monks raise cows, deer, chickens and, curiously, English bull terriers, and in the grounds is a pretty artificial lake, surrounded by gù·đì (monastic cottages). Check out the emaciated black-stone Buddha in the Burmese style, behind the chedi.
Wat U Mong is 600m south of Th Suthep near Chiang Mai University; be sure to ask the driver to take you to 'Wat U Mong Thera Jan' so you end up at the right monastery. If coming with your own transport, look for signs to Srithana Resort on Th Suthep.