# Gunung Mulu — the caves whose records keep moving Canonical: https://sockmonkey.com/places/gunung-mulu (this is a plain-text copy of that page) Source: https://sockmonkey.com/places/gunung-mulu Publisher: SockMonkey.com (https://sockmonkey.com) Part of: The Field Guide - https://sockmonkey.com/places/ Cite as: SockMonkey.com - sockmonkey.com Last reviewed: 24 October 2026 - **Where:** Miri Division, Sarawak, northern Borneo, Malaysia - **Coordinates:** 4.0400° N, 114.8200° E - **Biome:** Lowland and montane rainforest, limestone karst, moss forest - **The park:** 52,864 ha; no road access, four show caves open to visitors - **Caves:** At least 295 km explored - **Status:** UNESCO World Heritage, 2000 - **Best visited:** Year-round; it rains, in every month ## The short answer Gunung Mulu National Park lies in the north-east of Sarawak, the Malaysian state on Borneo, close to the border with Brunei. It covers 52,864 hectares of rainforest around three mountains: Gunung Mulu itself, a sandstone peak of about 2,376 metres, and the limestone massifs of Gunung Api and Gunung Benarat. UNESCO calls it the most studied tropical karst area in the world. Beneath it lie at least 295 kilometres of explored cave, among them the Sarawak Chamber, Deer Cave and the Clearwater system. The park was gazetted in 1974, named an ASEAN Heritage Park in 1984, opened to the public in 1985 and inscribed as a World Heritage Site in 2000. No road has ever been built to it, by policy: visitors arrive by air, or by a long river journey, and around ninety per cent of the park and ninety-five per cent of its caves are closed to visitors except for research. ## Why it's worth knowing Mulu is a place of records, and the records are the least reliable thing about it. UNESCO’s statement of the park’s value, written for the inscription, says that Deer Cave is the largest cave passage in the world known at the present time. It was, when that was written. In 2009 a British-Vietnamese expedition surveyed Hang Sơn Đoòng in central Vietnam and found a larger one — the library’s own entry on Son Doong covers it. The same statement gives the Clearwater Cave system 110 kilometres of mapped passage. Expeditions kept connecting it to its neighbours: 102 km by 1991, 129 km by 2005, around 226 km by 2017, and 265.9 km by a count of November 2025, which puts it seventh on published lists of the world’s longest caves. The number in the official record is less than half the cave that is there. And the Sarawak Chamber, which UNESCO describes at 600 by 415 by 80 metres and 12 million cubic metres, was laser-scanned in 2011 and came out at about 9.6 million cubic metres — while a chamber in China, the Miao Room, has since been reported to be larger by volume. The Sarawak Chamber is still described as the largest known cave chamber by floor area. None of this makes Mulu less extraordinary. It makes it a place still being measured, by expeditions that have been coming back since 1977, in a park deliberately kept hard to reach. The superlatives are the part that dates. The caves, the forest and the bats at dusk are the part that does not. ## The field notes ### Deer Cave, and the exodus Deer Cave — Gua Rusa, named by the Penan and Berawan for the deer that came to lick the salty rock — is reached by a three-kilometre plank walk through the forest from park headquarters. The 1978 Royal Geographical Society expedition measured a section 174 metres wide and 122 metres high. A 2009 survey by the Hoffman Institute at Western Kentucky University extended the known system to 4.1 km and recorded a cross-section of 169 by 125 metres in the southern passage and a ceiling of 148 metres in the northern one. The main entrance is 146 metres high. At its far end the cave opens into the Garden of Eden, a round valley of rainforest about a kilometre across, walled by limestone cliffs on three sides. The park says twelve species of bat have been recorded in the cave, and puts its colony of wrinkle-lipped free-tailed bats at between 2.5 and 3.5 million. Most evenings, usually between 5.30 and 6.30 pm by the park’s account, they leave the cave in a stream that twists over the forest for many minutes — a ribbon, a coil, a smoke — to feed on insects. A viewing area below the entrance exists for exactly this, and the swiftlets make the opposite journey at the same hour. ### The chamber that frightened its discoverers In January 1981, during the Mulu ’80 expedition, three British cavers — Andy Eavis, Dave Checkley and Tony White — followed a river passage into a cave now called Gua Nasib Bagus, Good Luck Cave, and came out onto a boulder floor in a space their lamps could not reach across. One of them later described the experience as agoraphobia, underground. Early measurements gave it as 600 metres long, 415 or 435 metres wide and 80 to 115 metres high, depending on the survey. The 2011 laser scan gave 9,579,205 cubic metres and 164,459 square metres of floor. It was estimated at the time as three times the size of the Big Room at Carlsbad Caverns, then thought the largest underground chamber known. It is not a show cave. Getting there means following an underground river upstream, with swimming and a ledge traverse. The park arranges accompanied visits for experienced and properly equipped people, and they are the most demanding thing Mulu offers. ### The Pinnacles High on the flank of Gunung Api, rain has dissolved the limestone into a forest of grey blades, some of which the park describes as up to fifty metres tall. It is one of the most photographed landscapes in Borneo and it is earned. The trip is three days. A longboat on the Melinau river, a walk of about nine kilometres to Camp 5, a basic forest shelter with no doors or windows that holds 38 people a night; then, before dawn, a trail the park describes as 2.4 kilometres long and rising 1,200 metres, the last part near vertical on ropes and bolted ladders. The park calls it an extreme climb, not a trek, requires a licensed guide, and does not take anyone sixteen or younger. The descent, it warns, is often harder than the way up. ### The road that was never built When the park was gazetted in 1974, the Sarawak government chose not to build a road to it, and has kept to that. It is the single decision that most shapes the place. The great 1977–78 Royal Geographical Society expedition — more than a hundred scientists in the field over fifteen months, and the start of the Mulu Caves Project that continues today — worked from a base camp three days upriver from Miri. There was no airport then. There is now, but the forest is still bounded by rivers rather than tarmac, and the old route out on foot, the Headhunters’ Trail, follows a Kayan path to the Limbang side. The land around the park is lived in and contested. The Penan, once nomadic, are now semi-settled near its south-western edge; the Berawan keep hunting rights in the area. In 2019 Penan and Berawan communities blockaded a logging company working near the park and lodged a complaint with UNESCO. The Sarawak government said the logging would not affect the park. The complaint is on the record either way. **A relic from Gunung Mulu** The entrance to Deer Cave, 146 metres high. In the late afternoon, below it, a dark thread appears against the sky, thickens, and begins to twist — millions of wrinkle-lipped bats leaving the mountain to feed, in a stream that coils and loops over the canopy for many minutes. It happens almost every evening, weather permitting, and not on command. Rain can cancel it, which is why a sensible plan allows two evenings. ## Getting there How to get there. Fly. MASwings, part of the Malaysia Airlines group, flies into Mulu’s small airport from Miri on the Sarawak coast (about thirty minutes), Kuching (about an hour and twenty minutes) and Kota Kinabalu (about fifty-five), by the park’s figures. The park warns that heavy rain occasionally cancels flights. The alternative is river travel from Marudi up the Baram and Tutoh, which is slow, needs arranging in advance, and has no regular service. Permits and guides. Every visitor needs a park permit, and the show caves — Deer, Lang’s, Clearwater and Wind — are visited with a park guide in small groups at set times. Adventure caving, the Pinnacles and the Headhunters’ Trail are booked through the park or licensed operators, and Camp 5 has limited beds: book the Pinnacles well ahead. Timing a visit. Two or three nights is the minimum to see the show caves and the bat exodus without rushing; add three for the Pinnacles. The park says the bats leave on most evenings between 5.30 and 6.30 pm, on rare occasions not at all, so plan more than one evening for it. When to go. Mulu receives four to five metres of rain a year, under the north-east monsoon from about December to March and the south-west from about May to October, and it rains in every month. The park says it can be visited all year: mornings usually dawn clear, and rain typically comes between 1 and 5 pm. It names June to September and holidays as the busiest times. The caves themselves are indifferent to the weather. Staying. Accommodation is at park headquarters, in homestays in the villages nearby, and at a large resort by the park entrance. Bring a headlamp, insect repellent, clothes that can stay wet, and shoes with grip for the boardwalks. ## Common questions #### Is Deer Cave the largest cave passage in the world? Not any longer. Deer Cave in Gunung Mulu National Park was long regarded as the largest cave passage known, and UNESCO’s statement for the park still describes it that way. In 2009 a British-Vietnamese expedition surveyed Hang Sơn Đoòng in Vietnam and found larger passages. Deer Cave’s main entrance is 146 metres high and its passages reach 169 metres wide. #### How big is the Sarawak Chamber? A 2011 laser scan measured the Sarawak Chamber, in Gunung Mulu National Park, at 9,579,205 cubic metres and 164,459 square metres of floor. UNESCO’s statement gives older figures of 600 by 415 by 80 metres and 12 million cubic metres. It is described as the largest known cave chamber by area; the Miao Room in China has been reported as larger by volume. #### Who discovered the Sarawak Chamber? Three British cavers, Andy Eavis, Dave Checkley and Tony White, in January 1981, during the Mulu ’80 expedition. They reached it by following a river passage into Gua Nasib Bagus, Good Luck Cave, in Gunung Mulu National Park, Sarawak. It was estimated at the time as three times the size of the Big Room at Carlsbad Caverns. #### How long is the Clearwater Cave system? The Clearwater Cave system in Gunung Mulu National Park measured 265.9 kilometres in a count of November 2025, placing it seventh on published lists of the world’s longest caves. Its length has grown as expeditions connected it to neighbouring caves: UNESCO’s statement for the park gives 110 km, and published figures pass through 129 km in 2005 and about 226 km in 2017. #### How many bats live in Deer Cave? Gunung Mulu National Park says twelve bat species have been recorded in Deer Cave, and estimates its wrinkle-lipped free-tailed bat colony at between 2.5 and 3.5 million. The bats leave the cave in a long twisting stream on most evenings, usually between 5.30 and 6.30 pm, and a viewing area below the entrance is provided for watching it. #### Can you drive to Mulu National Park? No. The Sarawak government has kept Gunung Mulu National Park free of road access since it was gazetted in 1974. Visitors fly to Mulu’s airport, most often from Miri, a flight of about thirty minutes, or travel by river from Marudi, which has no regular service and must be arranged in advance. #### How long and how steep is the Mulu Pinnacles trail, according to the park? The park describes it as an extreme climb rather than a trek. The trip takes three days: a boat ride and a walk of about nine kilometres to Camp 5, then a trail of 2.4 kilometres rising 1,200 metres, the final section on ropes and bolted ladders. A licensed guide is compulsory, the park does not accept anyone aged sixteen or under, and it warns that the descent can take five hours or more. #### How much of Mulu National Park can visitors see? A small fraction by design. About ninety per cent of Gunung Mulu National Park and ninety-five per cent of its caves are closed to visitors except for research. Four show caves — Deer, Lang’s, Clearwater and Wind — are open with park guides, along with a canopy skywalk, forest trails, the Pinnacles climb and a number of adventure caves for equipped groups. What to pack: the Rainforest & reef kit, forest, caves and waterfall trails ## Related places Danum Valleyabout 340 km away · both tagged rainforest Kampong Ayerabout 100 km away · same region El Nidosame region · same access level (2) Côn Đảosame region · same access level (2) Ifugao Rice Terracessame region · same access level (2) Notes on sources. This entry draws on UNESCO’s World Heritage listing and statement of Outstanding Universal Value for Gunung Mulu National Park, quoted on the page for the figures it gives; on the official Mulu National Park website for the Pinnacles climb, Camp 5 and visitor rules; on published accounts of the Mulu Caves Project and its expeditions, including the 1981 discovery of the Sarawak Chamber and the 2011 laser scan; on the 2009 Hoffman Institute survey of Deer Cave; and on published reference material for the park’s history, access policy and the 2019 blockade. Records are reported with their dates, because they have moved. Deer Cave is described by UNESCO as the world’s largest known cave passage, a status superseded by Hang Sơn Đoòng in 2009, per this library’s Son Doong entry. Clearwater’s length appears as 110 km (UNESCO), 102 km (1991), 129.4 km (2005), about 226 km (2017) and 265.9 km (November 2025). Sarawak Chamber dimensions appear as 600 × 415 × 80 m and 600 × 435 × 115 m; its volume as 12 million m³ (UNESCO) and 9,579,205 m³ (2011 scan). The Miao Room’s larger volume is reported as claimed, not verified here. Gunung Mulu’s height is given as 2,376 and 2,377 m. The Deer Cave bat colony is estimated at about three million and at about two. The Pinnacles’ height of up to fifty metres is the park’s own figure. Travel advisory: the United States has Malaysia at Level 1, exercise normal precautions; the increased-caution area is the islands and coastal waters of eastern Sabah, which do not include Sarawak. Checked 28 September 2026. Re-checked on 24 October 2026. The park’s official site (mulupark.com) was read directly: its Pinnacles page (2.4 km rising 1,200 m, pinnacles up to 50 m, Camp 5 for 38 guests a night with no doors or windows, the 9 km walk from Kuala Litut, a licensed guide required, not suitable for children 16 and younger, a descent of five hours or more), its Deer and Lang page (a 3 km plank walk), its bat exodus page (twelve species; 2.5 to 3.5 million wrinkle-lipped bats; most evenings between 17:30 and 18:30, rarely not at all), its plan-your-trip page (MASwings from Miri, Kuching and Kota Kinabalu with flight times; visitable all year; afternoon rain; June to September busiest) and its World Heritage page (Mulu summit 2,376 m). Wikipedia’s articles on the park (gazetted 1974, ASEAN Heritage Park 1984, opened 1985, 52,864 ha, 295 km of cave, 90 per cent of the park and 95 per cent of the caves closed except for research, four show caves, rainfall and monsoons, the 2019 blockade), the Sarawak Chamber (the 1981 discovery, the dimensions and the 2011 scan), Clearwater Cave (265.882 km, seventh longest, November 2025) and Deer Cave (the 1978 and 2009 surveys, the Garden of Eden) were read the same day. The bat colony had been given here as about three million or about two; the park’s range replaces both. The 1984 date some accounts give for the opening is the ASEAN Heritage Park designation. UNESCO’s list page refused the request, so its statement is quoted as previously read. Written and fact-checked by SockMonkey.com. Last reviewed 24 October 2026.