Sarawak Chamber and the Cave System in Mulu Caves
Part of the Mulu Caves travel guide — see every topic in All Mulu Caves Guides.
Mulu's caves are the reason for the UNESCO listing, and the numbers are hard to hold in the head. Sarawak Chamber, discovered in 1981 inside Gua Nasib Bagus, is the largest known cave chamber in the world by area — roughly seven hundred metres long, four hundred wide and seventy high, with a floor area that would hold several aircraft. Clearwater Cave is among the longest cave systems on earth, with well over two hundred kilometres surveyed and more being added. Both are the product of decades of British-led expeditions.
Sarawak Chamber
Found in 1981 by a British caving expedition working up an underground river passage, and immediately recognised as extraordinary: a single void of a scale that had no precedent. It is not lit and it is not a show cave. Access is by an adventure caving trip involving a long river approach, a strenuous crawl and climb through the entrance series, and then a walk across a boulder-strewn floor by headlamp in a space so large that a light beam does not reach the far side or the roof. It requires experience, a permit and a caving guide.
Clearwater and the through-systems
The Clearwater system is among the longest surveyed cave systems in the world, running for well over two hundred kilometres beneath the Mulu massif and still being extended by expeditions. Only a fraction is accessible on the show-cave boardwalk. Beyond it are river passages, dry fossil galleries, connections between separate cave entrances, and sections reached only by multi-day expedition caving. Mulu has been systematically explored since 1978 and the survey is genuinely unfinished.
Adventure caving
The park runs graded adventure caving trips beyond the show caves, from beginner to advanced. Beginner routes include Racer Cave and the Lagang Cave, involving scrambling, some climbing and getting muddy. Intermediate and advanced trips — Clearwater Connection, Sarawak Chamber, Turtle Cave — involve river swimming, long crawls, vertical sections and several hours underground, and require previous caving experience and, in some cases, a demonstrated level of fitness. All are guided, capped and booked ahead.
How it formed
The Melinau Limestone is a thick Eocene-to-Miocene formation, uplifted and fractured, sitting against older sandstone. Rainwater made acidic by soil and vegetation dissolves the limestone along joints and bedding planes; rivers running off the impermeable sandstone flow into the limestone and cut passages, and as the land rises those passages are abandoned and left dry while new ones cut lower. That is why Mulu has huge fossil galleries above active river caves, and why the Pinnacles stand above the same rock that is hollow beneath.
Sarawak Chamber and the Cave System at a glance
| Sarawak Chamber | Largest known cave chamber on earth — found 1981 |
|---|---|
| Dimensions | Roughly 700 m x 400 m x 70 m |
| Clearwater | Among the world's longest systems — 200+ km surveyed |
| Exploration | Systematic British-led expeditions since 1978, still ongoing |
| Adventure caving | Graded beginner to advanced; guided, capped, booked ahead |
| Geology | Melinau Limestone dissolved along joints by acidic rainwater |