The Deer Cave bat exodus is the reason most people come. From an observatory near the cave mouth you watch wrinkle-lipped bats leave in a dense, twisting ribbon that takes over an hour to pass, with bat hawks and peregrines picking birds out of the column. It is cancelled by heavy rain, so allow two evenings.

The show caves — Deer, Lang's, Clearwater and Wind — are among the world's largest, with Sarawak Chamber the biggest known cave chamber on Earth, though access to it is restricted to expedition caving. Swiftlets nest inside in vast numbers and navigate by echolocation.

The canopy walkway and forest trails hold the surface wildlife: gibbons calling at dawn, bearded pigs, squirrels of many species, and an excellent bird list including hornbills and trogons.

The night walks produce stick insects, tarantulas, tree frogs, and the huge diversity of invertebrates that limestone forest supports.

The Pinnacles on Gunung Api are the famous trek — a brutally steep climb to a viewpoint over razor-edged limestone blades, taking three days round trip and demanding real fitness.

The drier months make trails and river travel easier, but this is Borneo and rain is constant.

Practicalities

Mulu is reached by air from Miri or Kuching; there is no road. Park accommodation and the show cave tours should be booked in advance through the park, and the Pinnacles trek requires a guide and a permit booked well ahead.

The park is on the ancestral land of the Berawan and Penan, and guides from these communities run much of the operation.