In 1974, Mount Mulu and its surrounding areas were gazetted as national park by the Sarawak government. In 1978, the Royal Geographical Society organised a scientific expedition to the Mulu National Park, the largest such expedition ever to be dispatched from the United Kingdom. The expedition lasted for 15 months, in the course of which a small subgroup explored and surveyed 50 km of caves, including Clearwater Cave, Green Cave, Wonder Cave, and Prediction Cave. At that time, there was no airport and no logging roads available at Mulu. A base camp was established at Long Pala. The base was a three-day journey from Miri upriver. Thus the exploration of the caves in the western flank of Mount Api began. In December 1980, another British expedition team was dispatch to Mulu Caves for 4 months. In this expedition, Sarawak chamber, which lies in the Gua Nasib Bagus was discovered. In 1984, Gunung Mulu was designated as ASEAN Heritage Park. In 1985, the park was officially opened to public. In a British expedition in 1988, a link was established between Clearwater Cave and Cave of the Winds which extends the Clearwater cave to , claimed to be the longest cave passage in Southeast Asia. Blackrock Cave was also discovered during this expedition. In 1991, a connecting passage was discovered between Blackrock Cave and Clearwater Cave. This extends the Clearwater Cave passage to , leading it to be the 7th longest cave passage in the world. Between 1993 and 2000, British expedition teams explored the eastern flank of Mount Api with several discoveries made in the Hidden Valley.