Sikkim is a land of dramatic contours. Rugged mountains, deep valleys and dense forests consort with raging rivers, lakes and waterfalls to create a visual feast.  

• The state has the steepest rise in altitude over the shortest distance and has within its 7,096 sq. kms the entire climatic range, from tropical to temperate to alpine.  
• Located between these towering mountain ranges are passes like Nathu-la, Jelep-la, Cho-la and many others which were at one time important corridors of passage between Sikkim and Tibet. 

Source: NCERT – XI India Physical Environment