You can visit north sikkim , you will find highest lake Gurudongmar lake, and gangatok , nathula pass, pelling these are the best place to visit in sikkim
After visiting Gangtok (East Sikkim) and Nathula Pass etc, move to West Sikkim which offers more beautiful places such as Pelling, a quant town which has Asia’s second highest suspension bridge and Glass Sky Walk.
Pelling view of Kanchenjunga
Lachen monastery
Zuluk Panasonic views Yuksom beauty
Aritar greenery
Legship picturesque town
Yangtey paradise hamlet
Are some jaw dropping hill stations of Sikkim.
https://www.tripoto.com/sikkim/trips/things-to-do-in-sikkim-tourism-itinerary
Kindly check the above Tripoto link for more details.