Gomantong caves

The Gomantong Caves are an intricate cave system inside Gomantong Hill. The hill is the largest limestone outcrop in the Lower Kinabatangan area, Sandakan division, in the Malaysian state of Sabah, on Borneo island. Situated in a Sabah Parks forest reserve, the caves and the surrounding area are a protected area for wildlife, especially orangutans.
The cave system is home to many other animals, including massive populations of cockroaches and bats. Outside one can see crested serpent eagles, kingfishers, and Asian fairy bluebirds. Access is in the form of a wooden walkway circuiting the interior.

For centuries, the caves have been renowned for their valuable edible swiftlet nests, which are harvested for bird's nest soup. The most valuable of the nests, the white ones, can sell for very high prices.

Every evening, over 2 million resident bats spiral out for their evening feed. As the bats leave, the swiftlets are usually beginning to make their way back to the caves after a day's foraging. There are also bat hawks that linger not far from the scene and prey specifically on the bats as they leave their roost.

en.wikipedia.org/wiki/Gomantong_Caves