Bukit Lawang is the most popular base for organizing treks into the Gunung Leuser National Park, with plenty of guides based here. If you want only a short day-trek, a walk in the forest around Bukit Lawang is fine, and your chance of seeing monkeys, gibbons, macaques and, of course, orang-utans is high. A range of treks is on offer, including a week-long slog towards Ketambe in Aceh province, passing through some excellent tracts of primary forest. Increasingly, visitors are heading deep into the jungle to reach Tangkahan, which offers elephant-mounted treks and whitewater rafting. One of the most popular (and enjoyable) options from Bukit Lawang remains the full-day trek, which includes lunch and finishes with a thirty-minute trip to Bukit Lawang through the rapids on an inflatable tube raft. You must have a permit for every day that you plan to spend in the park, and you must also have a guide, and should also be careful when choosing – make sure they have ITGA approval. Guides supplied by the Jungle Inn have the best repuation. Whoever you decide to hire, they should never feed, touch or even call the orang-utans. Keep an eye out for the notorious Mina, a mischevious, semi-wild female known for intimidating visitors and occasionally descending from the trees to give chase.