Sikkim is to the north of West Bengal, adjoining Nepal to the west, China (Tibet) to the north and east, and Bhutan to the south-east. It is the second-smallest state and, with barely half a million people, the least populous.
Sikkim is very mountainous, with altitudes ranging from a subtropical 280 metres in the south up to the summit of Kanchenjunga, the world's third-highest mountain, on the north-west border with Nepal. Little of the land is useful for farming, but terracing has resulted in productive hillsides.
The main river is the Teesta, which drains the northernmost peaks and flows generally southward through the middle of the state, past Mangan and smaller towns, till it reaches West Bengal and flows south-west along the state border for some kilometres until near Kalimpong it meets its main tributary, the Rangeet, which drains much of the west.