Meru Nyingpa, Old Meru, situated behind the Jokhang temple inside the Lhasa Barkor, was one of the six temples built in the 9th century during the reign of King Relpachen by Nyang Shami Gocha. Restoration and renovation of the Jokhang, also called the Lhasa Tsuklakhang, had by then become an important activity for Songtsen Gampo's successors.
Destroyed by Langdarma, the temple was subsequently said to be rebuilt by Atisha and later became Geluk under the Third Dalai Lama Sonam Gyatso. It was damaged during the cultural revolution and restoration began in 1984.
It's a different complex from Meru Dratsang, also called Meru Sarpa.