Tumlong is a village in the Indian state of Sikkim in northeastern India. It is located in the Mangan sub division of North Sikkim district. it is on the bank of the Dik Chu river, a tributary of the Teesta River.

Rabdentse was the second capital of the former Kingdom of Sikkim from 1670 to 1814. The capital city was destroyed by the invading Gurkha army and only the ruins of the palace and the chortens are seen here now. However, the ruins of this city are seen close to Pelling and in West Sikkim district in the Northeastern Indian state of present-day Sikkim; Pemayangtse Monastery is one of the oldest monasteries in Sikkim which is close to the ruins. From the vantage point of this former capital, superb views of the Khanchendzonga ranges can be witnessed. This monument has been declared as of national importance by the Archaeological Survey of India. It was first established in 1670 by the 2nd Chogyal Tensung Namgyal son of the 1st Chogyal Phuntsog Namgyal by shifting from the first capital of Yuksom that was consecrated in 1642.