Monkha Sheri Dzong, one of 8 solitary places of Guru Rinpoche 

According to Guru's Khathang Deypa,
Monkha Sheri Dzong is one of the eight Sacred Neys of Guru Rinpoche
It lies on the border of Trashi Yangtse and Mongar.
Eight Sacred Neys mentioned in Khathang Deypa are:
1)Samye chemphu
2)Lhodrak Kharchu
3)Draki Yang Dzong
4)Yarlung Shel Gi Phu
5)Drak Mar Ya Ma
6)Monkha Sheri Dzong
7)Singye Dzong
8)Paro Taktshang Phug
It's said that the cliff from where the water(ThriChu) gushes out is like a Vase(Bumpa) and the rock on which it falls is like a mirror.
It's like performing Lhasang Thrisel.
Lhasang is the ritual of purification, cleansing people and places of any obstacles, obstructions and negative forces.