Sikkim is a beautiful place and if you want to explore all of it..you would require atleast 12 to 15 days. The major not to be missed places in sikkim are-
2. Nathula and Tsomgo Lake
3. lachen and lachung 4. gurudongmar lake and kala pathar
5. yumthang valley
6. Nacho and ravangla
7 temi tea gardens
9. Zuluk Incase you need any specific information..feel free to ask!!.