Hoollongapar Gibbon Wildlife Sanctuary, in Assam, is India's only sanctuary named after a primate: the hoolock gibbon. Spanning over 21 sq km of semi-evergreen rainforest, this compact reserve is one of the few places in the country where you can spot all seven of Northeast India's primate species, including the Bengal slow loris and capped langur. It's a haven for birdwatchers too, with more than 200 bird species, and is home to elephants, jungle cats, and diverse reptiles.
Apart from the gibbon, one can see capped langur, stump-tailed macaque, pigtail macaque, Assamese macaque, rhesus macaque and slow loris, elephant and so many other species of animals here.