There are daily flights from KLIA (KUL) or Kota Kinabalu (BKI) to Sandakan airport (SDK) by both Malaysia Airlines (MH) and AirAsia (AK). At Sandakan airport, there are two main options to get to Sepilok. The easiest one is by taxi. Otherwise, there are a number of public buses that go into the orang utan sanctuary. Journey will take about 30 minutes.
Note that if you hire a taxi, you may need to ask the driver to wait at the entrance for your return trip back to town. Additional cost may incur if you ask the driver to wait. On the other hand, taxi drivers rarely get into the sanctuary to pick-up passengers (it is about 3-4 kilometres off the main road, hence the drivers do not find it economical enough to expect returning passengers without prior notice). Local buses are quite OK, but probably not too reliable. The best is probably by local packaged tours.
This well-known sanctuary is one of the few orang utan's rehabilitation centres in the world. The others being in the Indonesian island of Sumatra, Semenggoh Wildlife Sanctuary near Kuching, and to certain extent, the Orang Utan Island in Bukit Merah Laketown Resort. If you are wondering why these sanctuaries are only located in South East Asian region, the answer is this: orang utans can only be found in Sumatra and Borneo (there are none in Peninsula Malaysia or Thailand, or Java, or the Philippines).
A rehabilitation center like Sepilok Orang Utan Sanctuary should not be mistaken with a regular zoo. Here, the orang utans are left in their natural habitat, which is the sanctuary's huge forest reserve where they can roam free, making nests on top of tall trees and feed on available natural resources (or fresh fruits provided by the staff).
The orang utans are adopted from nearby areas where their original habitats were displaced due to deforestation and rampant development (housing projects as well as palm oil plantations). Young ones are taken into the sanctuary, trained to survive in the wilderness before they are released back into the jungle.
The visitor centre here has the display of orang utans that have been released back into the wild - photos of them and their "nicknames". The visitor centre also hosts a video show to provide more information on the sanctuary's activities.
Important note:- The sanctuary is opened to public ONLY for about 2 hours everyday ie: during the feeding time of the orang utans. During my visit, the feeding time was around 1400 to 1600 hrs. Please do check with authority well ahead.
A must visit if you are in Sabah. Somewhat hard to get to (but once again, this is NOT a zoo).