The Tang Valley and Burning Lake
Stop first at the Burning Lake. According to legend, Terton Perma Linca had a vision that Guru Rinpoche had hidden some treasure in the lake. The people of the Tang Valley were naturally dubious, and so he held a butter lamp and dived in before re-emerging with the lamp still alight and chest of treasure. Do look out for the resident holy man who will show you around.
The Tang Valley is ideal to visit in October, when the valley turns bright pink when buckwheat flowers bloom, but is still a superb place to visit at other times of the year. Worth visiting is the Ugyencholing Manor which gives an amazing depiction into rural Bhutanese life and culture.