Bukit Lawang is located on the other side of Gunung Leuser National Park, about 4-5 hours drive from Medan. However if you are already in Tangkahan, there is a a shortcut , about 2 hours drive from Tangkahan to Bukit Lawang.
Bukit Lawang is famous for its Sumateran Orangutan ( Pongo abelii), one of the endanger mammals living in Gunung Leuser National Park. There was a rehabilitation center for orangutan here which was built for orangutan conservation, where young orangutans were taken care off and trained before released into the wild.
Now visitors can see orangutans in the wild, and must do trekking to the jungle for some hours to few days. I joined 3 hours jungle trail to see orangutan, started nearby Bukit Lawang Ecolodge and then walk uphill passing rubber plantation owned by private , and then proceed to the national park jungle. We met mother orangutan and the baby. They were so graceful climbing trees, and swing from one tree peak to another and hanging on lianas. Their balance and flexibility amazes me.
Before doing the jungle trek, be sure you wear long trousers and sleeves. And recommended to put mosquito repellent. It will be safer if you put the trousers end to the socks. Long sleeves are good to prevent leeches. And do not forget to bring water.
I do not think that feeding the orangutan is necessary, but usually local guides will use fruit to attract orangutan to come closer. Do not play or touch the orangutan.
Seeing orangutan in the jungle is not guaranteed. When there are abundant of food/ fruits in the jungle, usually not easy to find orangutan.
Other animals that visitors can see in the trail are: gibbons, kasuari bird, thomas leaf monkey.
If you love water activity, you can do rafting or river tubing in Bukit Lawang.
Most of the lodges are located nearby the river, my favorite place to eat in the area is Bukit Lawang Ecolodge Restaurant. It is tranquil and overlooking Bohorok River which is used by locals and even tourist to bath and enjoy.