Bukit Lawang is known for the largest animal sanctuary of Sumatran orangutan (around 5,000 orangutans occupy the area), and also the main access point to the Gunung Leuser National Park from the east side. Before going, you should know that orangutan sightings are not guaranteed as they are wild. Although they are peaceful creatures, try not to irritate them or provide them food.
Booking a trip well ahead with a reputed tour group is strongly recommended as it’s quite in a remote location from the airport itself (nearest airport Medan). You can contact the below tour operator who comes strongly recommended or do research for the tour operator of your liking.