Tagko lhakhnag is a community owned lhakhang. It was built in the 11th century by Nogpa Choki Dorji who was from Kham, Tibet. The oral history says that Nogpa Choki Dorji came to Thangbi from Sephu and meditated in a cave above the lhakhang. The lama is believed to have thrown the stone to find out where he should build his residence and the stone landed on the place where the current lhakhang stands today. It is believed that the lhakhang is built on the lake which caused harm to the communities in order to subdue the demons. Currently below the lhakhang, we can see the water flowing from the lake.