February - 2019

Hidden Valley, situated on the eastern flank of Api, presented unique difficulties for exploration. Significant discoveries had been made during the 1978 expedition but there remained great potential for more secrets to be revealed among the pinnacle karst of the Hidden Valley dolines. The remoteness of the area and inhospitable terrain made these the most challenging of all Mulu expeditions.

Hidden Valley from the east | photo © Rambli Ahmad

During January 1993 a six man team supported by Park guides and penan porters carried out a lightweight reconnaissance expedition into the Hidden Valley on the eastern side of Gunung Api. This was the first expedition to explore this area of the Park since the Royal Geographical Society expedition of 1977/8. The expedition aimed to cover as much ground as possible in the limited time available to gauge the potential for a future caving expedition to this area. A small and rather squalid camp was established in the centre of the Hidden Valley gorge between the entrances of Prediction Cave and Wonder Cave  and just above the flood plain. 

Prediction Cave was re-located and six other previously undocumented entrances were recorded. The weather conditons were dry and any water running into the gorge disappeared into sinks as soon as it hit the limestone. This left a dry river bed downstream of the camp which provided a useful highway to explore the  the bottom end of the valley.

Towering cliffs dominate the landscape | photo © Matt Kirby

A search around the walls of the gorge revealed some entrances which would require equipment to gain access, these were noted for future reference. At the western end of the gorge the ground rises up from an alluvial plain and onto a rugged and inhospitable karst landscape which is covered in dense vegitation. Exploration continued into this area which passes through a series of deep dolines. The first doline revealed nothing but in the second doline a cave was found and named Lawai’s Cave. This was later renamed Arch Cave. No exploration was carried out but this was noted as a significant find. Other small entrances were found in this area and it was thought likely that potential existed here for significant discoveries. 

Exploration stopped at the southern side of the second doline but it was known from aerial photography that the valley turns south from this point to cross more deep dolines before emerging high above Good Luck Cave in the Paku Valley.

Although no underground exploration was carried out during the three days which the team were in the valley, sufficient entrances had been found to justify a full scale expedition to the area.    



Expedition Members

The 1993 team   

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