The hilly virgin rainforest, part of the Sri Lanka lowland rain forests ecoregion, was saved from the worst of commercial logging by its inaccessibility, and was designated a World Biosphere Reserve in 1978 and a World Heritage Site in 1988. The reserve's name translates as Kingdom of the Lion.
The reserve is only 21 km from east to west, and a maximum of 7 km from north to south, but it is a treasure trove of endemic species, including trees, insects, amphibians, reptiles, birds and mammals.
Because of the dense vegetation, wildlife is not as easily seen as at dry-zone national parks such as Yala. There are no elephants, and the 15 or so leopards are rarely seen. The commonest larger mammal is the endemic Purple-faced Langur.
An interesting phenomenon is that birds tend to move in mixed feeding flocks, invariably led by the fearless Greater Racket-tailed Drongo and the noisy Orange-billed Babbler. Of Sri Lanka's 26 endemic birds (suranganet), the 20 rainforest species all occur here, including the elusive Red-faced Malkoha, Green-billed Coucal and Sri Lanka Blue Magpie.
Reptiles include the endemic Green pit viper and Hump-nosed Vipers, and there are a large variety of amphibians, especially tree frogs. Invertebrates include the endemic Common Birdwing butterfly and the inevitable leeches.