The Dungchen Menchhu flows through a tunnel in the middle of a cliff behind the Dagana Dzong. In the past, people used to spend nights, soaking themselves in the Menchhu heated with roasted stones. It is believed to cure headaches, stomach pains, joint pains and many other diseases. it is believe that If you drink the menchhu or wash or bathe in it with belief, it helps you.  

It is believed that Guru Rinpoche hid a long trumpet or Dungchen as a treasure inside the cliff. The Dungchen later flew away creating a hollow tunnel through which a menchhu started flowing out.

Cliff  where long trumpet or Dungchen hid a  as a treasure inside

It is believed that drinking or soaking in a menchhu cures various diseases. One such Menchhu is the sacred Dungchen Menchhu in Dagana. 

Dungchen in Chizi Goenpa

Chizhi Lam first noticed the treasure horn on the balcony, which was then placed as the main relic in Dekiling Lhakhang. Since the Lam was reigning over people of Genekha and Dagana at the time, according to his vision, he took the horn wherever he went and blessed the people. The horn, which is currently at Chizhi Goenpa in Thimphu, is opened to the public once every year on the eighth month of the traditional calendar.

Source:  BBS , Kuensel