Tourist circuit in Sikkim is centered around Gangtok. Three night package is enough to cover areas around Gantok. Two more nights and three days are required to cover Pelling area and if you plan to goto north Sikkim then minimum two nights and three days are required. For Indian tourist also permits are required to visit some boarder areas so keep two photos and identity proof for all your family members. Your travel agent will arrange permit for you.
Here are some details to help tourist visiting Sikkim. You can discuss with your travel agent and finalize your itinerary.
Pickup from NJP railway station / Airport and travel upto Gangtok (Alt 5500 ft)( 4 hours journey ), Afternoon cable car and evening at MG road , night stay at Gangtok
Start for Tsomgu Lake 12400 ft Baba mandir at 13500ft and Nathulla Pass at China Border ( 14400 ft ) , return to Gangtok in evening and night stay at Gangtok
Local sight seeing at Gangtok (here are the points) and night stay at Gangtok