Make the journey to Darjeeling, which is fairly isolated. It cannot be done by air at all, so you will already need to be in India. Main railways or an air flight can take you to Kolkata, where a train connection to Siliguri can be made. From here, either the classic Toy Train line (see Step 2) or a jeep-taxi can take you the rest of the way. For those following the overland route from Nepal, a jeep-taxi from the border will take you to Siliguri, where the rest of the route will be the same.
Take the Darjeeling Himalayan Railway, or "Toy Train," if not on the way up, then on the way back. This classic steam engine is something of a nineteenth century engineering marvel, and the most charming way to make the climb up to Darjeeling. It is a major tourist attraction in its own right, and is not to be missed.
Take in the views. The commanding heights of Darjeeling give a fantastic view of the surrounding slopes with their tea plantations, highland forests and villages. Off in the distance is Kanchenjunga, the third highest mountain in the world at 28,169 feet.
Visit the Darjeeling Zoo and the Himalayan Mountaineering Institute. The latter has some excellent specimens, from Himalayan leopards to the adorable Red Panda. If you have time for a stay of a few weeks, you might consider enrolling in mountaineering courses at the Institute, established by the famed Tenzig Norgay who, along with Edmund Hillary, was the first to climb Mount Everest (see Resources below).
Shop for crafts at the Tibetan Self-Help Center. Darjeeling is home to many Tibetan refugees, and the center sells handicrafts to finance social programs for them. It is a little more expensive than the tourist shops in town, but these curios are made locally, and not in an Indian or Chinese factory.
Shop for tea! One of the pleasures of Darjeeling for the tea lover is the privilege of being able to go out and explore a tea garden and then sample the product in a shop. The tea available on just about any cafe table is better than the best you have probably ever tasted, so even the uninterested should sample the local wares and bring some home (see Resources below).