About Hang Thung Cave
At the deep pool at the head of the collapsed doline 50m above and to the right two draughting entrances unite after 30m in a downwards sloping overflow passage. This soon enlarges dramatically in a massive 60m wide chamber with several static lakes. Cross one by a 30m swim to a 9m climb up. Above a smaller passage floored by fine gours is followed to where daylight can be seen. A short swim is needed to cross a big gour to the continuing rift passage. This passes below a 25m shaft (daylight) a short slope down to a 16m pitch with a rebelay at 4m. This fine pitch lands in a deep lake with the sound of a river in the distance.
A 70m swim soon reaches the main river, flowing over rapids in a clean washed passage over 30m high. Over the next 500m, gour pools are crossed by swimming, interspersed with rapids. A massive collapse is reached which is easiest to cross on the left hand side. Several short climbs are required to cross from boulder to boulder often over 30m long. A short section under two huge blocks leads into a huge area where the right hand wall is not seen. Traversing up over a sloping slab leads to a 3m diameter stal boss with a dribble from the ceiling 20m above. The collapse eventually leads back to the river and several more pools. A second shorter collapse is crossed above and a third is passed by swimming below a boulder. A section of elliptical passage sloping down from the right follows, with easy going on a clean washed floor to the right of the river. A dribbly inlet enters down a flowstone slope on the right.
Another big collapse follows, with the sound of roaring water ahead. Up a slope to the right here leads to brilliant gours and stals and a devious route to a balcony 30m above the river in a passage 1m wide. The best route is to climb about 3m above the water and squeeze through boulders back down to the river. A short arched duck follows into fast flowing canal.
50m forward the stream roars down a canyon about 1m wide. Progress is made by pulling along the walls until a very turbulent section is passed by a precarious traverse above the water. A fall here would be very serious. Around a bend the entire river falls from a 2m high cascade into a spray filled chamber. Fortunately a rift short cuts this section with an upwards 10m climb to a spacious lake chamber, the water falling away on the right hand side. A further swim leads to a series of rapids and a point where the passage is split by a high rock island, the river flowing to either side. To the right, a swim against the current leads to where it is possible to climb up onto the ‘island’. This allows a traverse on one wall with the rapids below, to another big lake chamber. Crossing this more rapids leads to a large stal portcullis with a passage above. This is about 1750m into the cave.
Continuing on an area of rapids is then passed to a long swim of about 300m. This narrows, and blocks in the water give a fighting chance against the considerable current. The river flows down a ramp from the left and the only way around this is to be flattened against the opposite wall for 10m until a niche allows a climb up above the water. A chamber with one wall formed from a detached flake over 30m long and high leads back down to a quieter canal area. The passage is more rift shaped with darker walls in this region of the cave.
The canal speeds up once again; progress is by following one wall until a further collapse provides a rest. A squeeze through blocks allows this to be surmounted and a big boulder pile followed down slope. This leads to an elbow bend to the left, with a 10m climb up the side of a big perched block. The river is seen again on the left, flowing down a series of noisy rapids. Traversing to the right on blocks leads to more rapids in the water and yet another lake. Gloomy swimming in a very wide dark canal ensues for 200m around several wide bends, with the route not obvious due to the size of the passage. Finally it is possible to land on a rock floor sloping up for 30m into a lovely polished rock overflow. The river comes from below the blocks in a large passage off to the right. This is around 2850m into the cave.
The passage to the right sumps after a further 70m of swimming. A 3m free dive enters a small airbell and continuing sump. Entering the overflow, a fine canyon ascends at 30 degrees, then flattens out and is floored by deep, clear pools. After 140m, this intersects a much larger gallery sloping from left to right, with a small stream in the floor. Downstream to the right, the passage dips into a deep lake almost immediately, a 40m swim to the far side revealing no above water continuation. To the left, the passage gradient flattens and a big slope of gours can be followed to the left, the passage being about 60m wide here. A small inlet enters down flowstone on the left, bats are seen entering here, but it quickly becomes too tight for humans. A rift beyond the passage slopes downwards once again, a deep gour necessitating a short swim. A fine staircase of gours is descended to the edge of a lake. This is crossed after 35m to the inevitable sumped continuation. The total length of Hang Thung is 3,351m and with over 6k to the known sink much more cave passage awaits discovery.
Hang Thung is a truly remarkable cave being one of the most sporting and challenging caves we have ever discovered in Vietnam. Superb situations and fabulous decorated huge cave passage make this cave to many of the people who were fortunate to be on the discovery the best cave they have ever been involved in exploring.