Sikkim
Gangtok
Gangtok is where most Sikkim trips begin, and its real value is as a base rather than a destination.
The town itself is a steep ridge of concrete with one pleasant pedestrian street, MG Marg, where no vehicles and no spitting are allowed and the whole town walks in the evening. Rumtek monastery, half an hour out, is the seat of the Karma Kagyu lineage and the more worthwhile hour. Enchey, closer in, is quieter still.
Tsomgo lake and Nathu La are the standard day trip. Both need permits arranged through a registered operator in Gangtok, both are high — Tsomgo is at around 3,700 metres — and Nathu La is closed to foreign nationals entirely. If you have only been in the hills a day, that altitude gain in a single drive is a lot.
For actual Sikkim, keep going. Pelling for the Kanchenjunga view, Yuksom for the walking, north Sikkim for Lachung and the Yumthang valley — all of which need their own permits.
March to May and October to early December. The monsoon here brings serious landslides and roads close for days at a time.
Delightfully cool daytimes under open sunny skies with wild orchids in bloom.