Sure, I'd be happy to help you plan your 3-day itinerary in Gangtok! Here's a suggested itinerary:

Day 1:

• Start your day with a visit to the Enchey Monastery, one of the oldest and most important monasteries in Gangtok.
• Next, head to the Namgyal Institute of Tibetology, which houses a vast collection of Tibetan artifacts and literature.
• After that, take a stroll through the beautiful flower gardens at the Ridge Park.
• In the evening, visit the MG Marg, the main shopping and dining area in Gangtok. You can enjoy some local cuisine and shop for souvenirs.

Day 2:

• Begin your day with a visit to the Rumtek Monastery, located about an hour's drive from Gangtok. This monastery is considered to be one of the most important Buddhist centers in the world.
• After that, head to the Banjhakri Falls, a beautiful waterfall surrounded by lush greenery.
• In the afternoon, visit the Tashi Viewpoint, which offers stunning views of the Himalayas.
• In the evening, you can explore the local markets and try some street food.

Day 3:

• Start your day with a visit to the Tsomgo Lake, a glacial lake located about 40 km from Gangtok. The lake is surrounded by snow-capped mountains and is a popular tourist spot.
• After that, visit the Baba Harbhajan Singh Temple, a shrine dedicated to an Indian army soldier who died near the Nathu La Pass.
• In the evening, you can take a cable car ride to the top of the Gangtok Ridge and enjoy panoramic views of the city.

I hope this itinerary helps you plan your trip to Gangtok! Let me know if you have any other questions or need further assistance.