North
Even though the northern parts have a lot of riotreports lately it hosts some very good diving and snorkelingspots around the islands of Pulau Weh and Breueh, just outside Banda Aceh.
A bit further down you will find Leuser National Park where you can visit orangutans on their way out to the place where they belong - the djungle. Orangutans who has been illegally kept in captivity from all over Indonesia are staying at the rehabilitationcenter before they can manage to live by themselves out in the rainforest.

Central and West
In the middle of Sumatra on the western side you can see the Minangkabau architecture and view the pleasant surroundings of Bukittinggi. On your way down here you will pass the equator. This area is also the right place to try the Padang food, rendang is a must.

South
On your way down south you can stop by and take a ride at some of the sumatran elephants that lives in the Way Kambas National Park. If you want to take a close look at the famous vulcanic island of Krakatau you can get there by a speedboat from Bandar Lampung.