The Tongsa Gompa is the oldest monastery in Kalimpong, founded in 1692 by Tibetan and Bhutanese lamas at a time when this part of the hills was under the Kingdom of Bhutan. The current building stands on the ruins of the original structure and belongs to the Drukpa Kagyu school of Tibetan Buddhism, the same tradition that is the state religion of Bhutan.
The monastery is compact and less visited than the Tharpa Choeling, which means you can often have it largely to yourself. The interior has painted murals and traditional butter lamps, and the monks are generally willing to show visitors around. It is located in the lower part of town, and is a manageable walk from the main bazaar area. Combined with the nearby nurseries and the walk down to the old market, it makes a good morning's exploration.