The Forest Temple - Wat Umong

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Wat Umong (or ‘tunnel temple’) is a 700 year old Buddhist temple in Chiang Mai, Thailand. It is located against the mountains of Doi Suthep and is stationed behind a small open zoo. The temple was built in 1297 by King Manglai of the Lan Na dynasty. The temple was abandoned for many years before being reoccupied and restored in the 20th century. That may explain why some parts of the temple are in ruins and, after rainy season, the temple looks overgrown with moss. The entire Wat Umong complex consists of 15 acres of wooded grounds. Past the main complex, you can walk down towards a small lake where you can feed the fish and turtles. There's also a number of friendly pigeons that'll fly towards you. 

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The wat is famous for its ancient tunnels and large stupa. An artificial earth mound in the temple grounds covers a series of underground passageways that lead you around and eventually to the top level of open spaces and a large stupa. The purpose of these tunnels add to the temple’s mysterious air. A famous legend says that these tunnels were supposedly built by the King and painted with bush scenes so they could keep a famous but mentally deranged monk within the grounds of the monastery as he had a habit of just wandering off into the bush for days on end. 

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Some other attractions that you'll find in the wat includes Buddha field of broken sculpture, a fasting Bodhisatva, a Spiritual Theatre of paintings similar to those at Suan Mokkh, reproductions of ancient Buddhist sculpture of India, and a library-museum. Wat Umong is unique in that the resident monks live in a very natural setting, and occasionally feed the deer that live in the area. It's also possible to practice meditation at Wat Umong and to learn from the Monks.

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Sources: 1, 2, 3