The dzong is on a thin promontory overlooking the confluence of the Drangme Chhu and the Gamri Chhu. It was built in 1667 by Mingyur Tenpa, Bhutan's third desi. The entire eastern region was governed from this dzong from the late 17th century until the beginning of the 20th century. Several tame jaru (ghoral; mountain goat) roam the exterior courtyards. At the time of writing the dzong was undergoing significant renovations and was closed to visitors.
This dzong is unusual in that both the administrative and monastic bodies face onto a single dochey (courtyard). By the entry gate look left for the fine mani lhakhang and its slate carving of Seng Doma, a local protector who is half-male, half-female.
Inside are a half-dozen lhakhangs, though what you get to see will depend on which monks are around. The 1st-floor goenkhang features paintings of a yeti, while another chapel is dedicated to the deity Choegi (Yama) Gyelpo, the wrathful aspect of Chenresig. He is a protector of the faith, the god of death and the king of law, who weighs up the good and evil at the end of a person's life.
Many lama dances are performed in Trashigang to appease Yama, especially during the three-day tsechu in November/December, which also includes the unveiling of a large thangka and the displaying of a statue of Guru Rinpoche on the last day.