The Night Safari is the world's first nocturnal zoo and is one of the most popular tourist attractions in Singapore. The concept of a nocturnal park in Singapore was suggested in the 1980s by the former executive chairman of the Singapore Zoo, Dr Ong Swee Law. Constructed at the cost of S$63 million, the Night Safari was officially opened on 26 May 1994 and occupies 35 hectares (86 acres) of secondary rainforest adjacent to the Singapore Zoo and Upper Seletar Reservoir. The Night Safari currently houses over 2,500 animals representing over 130 species, of which 38% are threatened species. The Night Safari is managed by Wildlife Reserves Singapore, and about 1.1 million visitors visit the safari per year. The Night Safari received its 11 millionth visitor on 29 May 2007.