About an hour's drive from Lahad Datu, this 1120-sq-km reserve consists mainly of lowland dipterocarp forest with mangrove areas – most of it is technically secondary forest, but that doesn't seem to trouble the wildlife or visitors. The stars here are the elephants and primates – gibbons, red-leaf monkeys and macaques, plus a lot of orangutans. Rescued orangutans from Sepilok are released here, so you've got a pretty good chance of spotting some.
Mammals that you'd be very lucky to see include the shy clouded leopard, tarsier, slow loris and porcupine. Sadly you're unlikely to see the Sumatran rhino; the only two remaining specimens are kept away from visitors. Birdlife is particularly abundant, with a staggering 253 species recorded here, including all eight of the hornbill family, from rhino through to helmeted, and some naturalists come for the frogs and toads alone: the nocturnal croaking chorus consists of 71 species.