Hi Vipin, Sikkim is amazing in December. You can check out Gangtok, Yumthang Valley, Tsongmo Lake, Lachung, and several other beautiful places. Read more about them and explore more places in the trips and guide attached below.
GANGTOK FULL DAY CITY TOUR
Nathula Pass
TSOMGO LAKE & BABA MANDIR
GANGTOK-LACHUNG-ON THE WAY SEIGHT SEEING On the way to lachung do not miss Seven Sister Waterfall and Singhik View Point. Also, visit the Chungthang confluence on your Sikkim holiday tour where the Teesta River meets with the gushing Lachung River and the Lachen River, casting a spell over you. Chungthang Dam, Bhim nala falls(also known as Amitabh Bachchan falls).
Lachung
Sikkim indeed is small hilly state with a developing economy , the capital being Gangtok . Now there are ample places to visit in Sikkim .Gangtok is largest city . You can reach all the other places in Sikkim from Gangtok . You can visit pelling , Namchi , Ravangla , Aritar , Lachen and lachung . Gurudongmar lake is quiet an attraction in North Sikkim . Nathula pass, changu lake , Baba Mandir etc are frequented by tourists . So basically there are ample places to try out in Sikkim out of which my personal favourite being Ravangla . Thank you