The Nathula Pass around two hours drive from Gangtok. Wear sweaters even in summer because there may be sudden drop in temperature. Winter is very cold and may even drop down to - 20/ -25. So special clothing is required.
The above picture is of the temple of Baba Harbajan Sing. He was a soldier in the Indian Army and while taking the supplies he died in an landslide & flood. It is believed he is still guarding the border. The temple is at 13,000 feet.