Moreover, many people may be curious about what makes the Son River different from other rivers and streams nearby. In fact, sailing slowly on the deep-blue river helps tourists to forget all their sorrow and reach a fanciful world. Besides, only traveling on the Son River can give them the best view of a long range of imposing mountains in Phong Nha Cave.

The Son River is well-known for the diversified kinds of fish flocking into the river from the Phong Nha-Ke Bang Cave. Dragon-shaped boats with two drivers can be hired for the journey into the caves. The drivers usually row by hand when the boat gets deeper into the cave. An umbrella on the vessel is opened so that travelers can feel the slightly cooler temperature in the dim light and foamy waves. The scenery is like a private, mysterious world.

Some tour guides believe that it is good luck to be splashed by a water drop from the cave ceiling, although in truth it is difficult to avoid getting wet when sailing inside the cave.

The Son River is geographically part of the underground river of Phong Nha Cave, stretching 44 kilometers into the neighboring country of Laos. It has been graded as the most valuable cave in the world by the British Cave Research Association (BCRA) for four outstanding features: namely longest underground river, highest and largest cave mouth, prettiest and broadest sand beaches and most beautiful stalactites. Furthermore, Phong Nha-Ke Bang National Park was recognized the World Heritage Site by UNESCO in the year 2003.

Phong Nha Cave was discovered inside the Ke Bang limestone mountain at the end of the 19th century. Champa scripts carved on steles and altars were also found inside the cave. Whose dry grotto was named Bi Ky in 1992 when some 15 BCRA explorers conquered the 7,700 meter Phong Nha Cave in 34 days.

Although only a kilometer of the cave has been exploited for tourism, Phong Nha remains an attraction thanks to its mystery and hidden charm. In the darkish scenery the imagination of tourists can turn stalactites and stalagmites into many kinds of animals, an imperial palace, or even a pillar inlaid with sparkling gemstones.

Returning on the Son River, where the water ebbs and flows around the boat in very fascinating green color, tourists always look back at the triangular mouth of the cave which has garnered the attention of thousands curious people.