From Rigpa Wiki
Drakkar Tashiding (Wyl. brag dkar bkra shis sdings) - the most sacred place in Sikkim, visited by Guru Rinpoche in the 8th century, and in the 14th century by the tertön Rigdzin Gödem (1337-1408), who established a monastery there.
It is generally thought that Buddhism was introduced to Sikkim by Guru Rinpoche. He also blessed the land and consecrated many places in Sikkim, and blessed Tashiding as the land's spiritual centre. In the four directions around Tashi Ding are the four sacred caves of Guru Rinpoche.
As one walks up to the monastery (about half an hour), a little before reaching the top of the hill where the monastery stands, a small path branches to the left leading to a nearby Shitro cave. On top of the hill is the monastery established by Sempa Chenpo Puntsok Rigdzin and his grandson Sempa Chenpo Rinchen in 1641. Inside the main temple there are two stupas containing relics of these masters.
Behind the temple is a stupa cluster. It was in Tashiding that the cremation of Jamyang Khyentse Chökyi Lodrö was performed and that a stupa was built by his own disciples, including Dilgo Khyentse Rinpoche, to house his relics. It was later gold-leafed by Orgyen Tobgyal Rinpoche in the 1990s. On the eastern side of the stupa cluster is a self-manifested engraved Guru Rinpoche image (you need to ask for the key to the small shrine that houses it).