Trekking in Sikkim & Darjeeling:
Treks which are in the Indian state of Sikkim or part of Darjeeling (and Kalimpong) in West Bengal. When we think a trek in Eastern Himalayas, probably it will be in either Sikkim or Darjeeling.
Being geographically connected, Sikkim and Darjeeling are similar in many aspects. Be it weather wise or culturally.
The area has significant amount of international border and protected forest areas. So it has its related permit procedures. Check here to know various permits that you require for trekking in Sikkim.
Below are the diversified trekking options in this relatively smaller region from which you can surely pick one as suits your taste.