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Southeast Asia’s porous limestone geology presents spelunkers with infinite crevices, chasms, caverns and underground rivers to explore. Caves from Indonesia to Laos can challenge the experienced and amaze adventurous tourists.

Caves drill throughout Indonesia, especially Java. Among the best known are the 20-kilometer Luweng Jaran and Gua Barat’s underground river system, the longest in the southern hemisphere. Sewu boasts over 600 caves, and near Yogyakarta, the 1,200-metre Cerme Cave with a cool stream once served as an Islamic meeting hall.

Flores Island’s Liang Bua Cave has been attracting more visitors – and archaeologists – since the 2003 discovery of bones from an unknown, meter-tall humanoid. The “Indonesian Hobbits” (Homo floresiensis) along with their dinner, small elephant-like stegodons, vanished some 15,000 years ago.

Just as impressive, the Philippine’s UNESCO World Heritage Saint Paul Subterranean River National Park’s eight-kilometer waterway runs through a cave widening to 120 meters before emptying into Saint Paul’s Bay.

Cave systems wind through Samar Island, “The Caving Capital of the Philippines”, presenting sinkholes, underground rivers, caverns, mud rooms, waterfalls and natural bridges in caves over 20-kilometers long. Robin’s Cave, the country’s deepest, travels six kilometers on its descent to a depth of 190 meters.

Many of Malaysia’s major caves cut through Sarawak’s Mulu National Park. A four-hour jungle walk, steep climb and stream slog arrive at Sarawak Chamber, the world’s largest underground cavity.

A three-kilometer plank-way in Mulu leads to Deer Cave with countless bats fleeing at sunset, and a path to a sinkhole with vegetation sprouting in shafts of sunlight. Also in Mulu and accessible by boat, Simon’s Cave holds showerhead-like formations that actually sprinkle water during the rainy season.

In Thailand’s karst-filled Andaman coast, sea kayakers enter Viking Cave on Krabi’s Phi Phi Island to view ancient cave paintings of longboats, Chinese sailboats and elephants. Just north on Lanta Island, a forest trek leads to a small hole that descends to Khao Mai Kaew Caves.

Up in the kingdom’s northern Mae Hong Song province, cavers can inspect Tham Lod’s caverns and river tunnel. A third cave houses a prehistoric coffin and archaeologists discovered a 20,000-year-old human skeleton nearby. Thousands of birds put on a daily sunset show, flocking en-masse into the cave.

A 72-kilometer drive from Chiang Mai finds a roofed staircase climbing to Chiang Dao Cave. A fish-filled stream welcomes visitors in front of the cool crevice, in which stalactites, stalagmites and a reclining Buddha dominate.

Cambodia’s caving scene remains relatively unexplored, though the southern coast’s Phnom Slap Ta’aun in Kampot province hides a maze filled with limestone formations and underground domes.

Laos, on the other hand, has loads of accessible caves. In central Khammouane province, hosting the country’s highest concentration of caves, boats take travelers through the 7.5-kilometer Konglor Cave. In 2004, near the provincial capital, a farmer discovered Tham Pa Fa Cave with 229 ancient Buddha images, which can be seen after a short trek.

North of Vientiane in Vang Vieng, the four-kilometer Snail Cave was once used as an air raid shelter and a required guided tour includes a dip in a cool pool.

In Luang Namtha province near the Chinese border, tours to Kao Rao Cave, a series of five distinct chambers with masses of bats, limestone formations, and enormous passages, are led by local Hmong guides.

Viengxay “Cave City” in northeastern Houaphanh province served as the home for over 20,000 people and headquarters for the Lao revolutionary movement from 1964-1973, and has dozens of caves for every purpose with an audio tour to match.

The grottoes on the islands in Vietnam’s Halong Bay have been well-documented, but in 2009 the “World’s Biggest Cave”, Son Doong, was discovered, and follows a 2.6-kilometer river through spaces as wide as 138 meters.

South of Hanoi in Ninh Binh province, a rowboat navigates Tam C?c (Three Caves). Nearby, the Flute Wind karst, topped with a Buddhist temple, hides three caves with Buddhist statues and a breeze that emits a flute sound. Another relatively recent find (1974) in Cuc Phuong National Park in Thanh Hoa province was Con Moon Cave with evidence of Paleolithic and Neolithic man.

Caves in Southeast Asia? There are hundreds for every level of expertise and interest. It just depends on how low you want to go.

Vientiane-based Bernie Rosenbloom writes for TTG Asia, PATA Compass, and EcotourismLaos.com; and he co-authored The Responsible Tourism Guide to Cambodia, Laos and Vietnam.