West Sikkim is a district in Sikkim. The highlight of West Sikkim is the amazing Himalayan treks in the foothills of Mt Kanchenjunga (also spelt Kangchendzonga). The rolling mountains also offer some "low altitude" treks.
A special hiking permit is required for all high-altitude treks, and thus these treks must be organised through a tour guide. Travel to Yuksom and Pelling is allowed without a special permit (however the normal Sikkim permit is still required).
As for all destinations in Sikkim, the major mode of transport is "jeep", which refers to the ubiquitous 4x4 vehicles that plow around the hairpin bends. Times can be quite variable depending on road conditions, generally it takes 4-6 hours to travel from Gangtok to Yuksom or Pelling. Landslides and bridge repairs can make this trip take considerably longer. Locals catch the "share jeep", packing in 10 passengers, which is not recommended for those who highly value their personal space (however these are very cheap). Considerably more expensive is the "private jeep", but if travelling in a group this is often quite economical. From some destinations, if a direct jeep does not run, you may have to go via Geyzing, the major transport centre in West Sikkim (Geyzing is a short jeep ride down the hill from Pelling)
Jeeps can be hailed along main roads throughout the region, but if all 10 seats are full (which is common), you may have to ride on the back.
Yuksom, at the trailhead of the high-altitude treks is a beautiful town to spend a few days relaxing. It was previously the capital of Sikkim, and is considered a holy town. The 300 year-old Dubdi Gompa (Buddhist temple), perched on a hill, is well worth visiting.
Pelling, located on a hillside is another beautiful town with character. Many guesthouses offer breathtaking views towards Kanchenjunga from their balconies. Within walking distance (4-5km) of Pelling is the Pemayangtse Gompa (one of the holiest gompas in Sikkim), and Rabdentse (an old archeological site from when this was previously the capital).
Many people spend 5-7 days on a trek, then a further 2-3 days exploring Yuksom and Pelling.
The high altitude treks are highly recommended, and certainly compare favourably to those across the border in Nepal. Most of the high altitude treks start from Yuksom. All treks must be accompanied by a tour guide, who arrange a special trekking permit. The more popular treks either go to Zongri (4000m) or Gochela Pass (5000m). The Zongri trek usually takes 5-6 days, and the Gochela trek 7-8 days, though this varies depending on fitness and previous exposure to high altitudes. The region is extremely beautiful, with numerous photographic opportunities. Note that altitude sickness is a common concern in this region due to the relatively short distances required to gain significant altitude. A "rest day" for acclimitisation is strongly advised at Tsokha (3000m). Successful climbing to Gochela Pass usually involves leaving at 3AM on that morning to reach the pass for sunrise before the clouds sweep in. Porters, with the help of yaks and ponies carry most of your gear, but you should carry your own day-pack with water, snacks and warm weather gear. Note that temperatures can fall well below zero at any time of the year at high altitude, and you should either hire or take genuine cold-weather gear and sleeping bags(most tour companies will hire these). One of the more popular tour companies is Modern Tours (linked to Modern Central Lodge in Gangtok) -- they hire sleeping bags and jackets at no cost. Most tour agencies cost $30-35 USD per day (including transport, food, porters and an English-speaking guide).
Low altitude treks are also popular, and since an additional permit isn't necessary, these can be done at your own pace. The typical trek starts in Pelling, and finishes either at Yuksom (3 days 40 km), or Ravangla (4 days, 54 km). The route follows both roads and paths, and several guesthouses are available for accommodation along the way. The trek passes Khecheopalri Lake, 14 km from Pelling.
The delicious food combines Nepali, Tibetan and Indian styles. Highly recommended is the Tibetan momos (dumplings). Each town has several good restaurants.
Soft drink, beer and bottled water are cheap and widely available. The bold traveller can sample the dirt-cheap Sikkimese rum.
There are few safety concerns in the region -- people are generally quite trustworthy. There are considerably less touts and rip-off artists compared with lowland India.
Jeeps trips to Gangtok or Darjeeling in West Bengal are easily organised at the jeep stand, or pre-booked at several travel agents.