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The valley is hidden by time.
Hung Thoong (or simply Hung Thoong) is a cave system located in the core area of Phong Nha - Ke Bang National Park, in the former Quang Binh province, now Quang Tri province. This area is strictly protected and can only be accessed through controlled expedition tours; it is not open to independent tourism.
Hung Thoong is essentially a deep cave-valley ecosystem, almost completely isolated from the outside world. This system comprises many interconnected points such as Hung Cave, Tron Cave, Thung Cave, along with a network of underground streams and lakes within the caves.
In between are large sinkholes often called "Nightmare" - vertical caverns hundreds of meters deep, giving the impression that the mountain's interior has suddenly opened up.
The "dinosaur eggs" in Hung Cave, part of the Hung Thoong cave system.
The unique feature of Hung Thoong lies in the interplay of spaces: the clear blue lake within the cave, the narrow, dry sections of the cave, and the underground water connecting the areas, making the journey feel like traversing multiple layers of terrain within the same limestone system.
Every journey of discovery only begins when people leave their familiar comforts and venture deep into the primeval forest, climbing over sharp limestone rocks, swimming through flooded cave passages, and traversing isolated valleys to access parts of the cave system.
According to Trinh Tu, who spent three days and two nights exploring Hung Thoong Cave last May, the journey wasn't simply about "going to experience," but rather a process of the body having to adjust to the constantly changing terrain of the forest and caves.
The 3-day, 2-night trip to Hung Thoong begins with a trek through the primeval forest. From the very first steps, the terrain constantly changes.
The space was cramped by the dense forest canopy, allowing only small patches of light to penetrate. The forest floor was damp and slippery from decaying leaves. In some sections, we had to cling to tree roots to climb over rocky slopes; in others, we had to wade through cold streams that cut across the path; and in still others, we had to move slowly to avoid slipping on moss-covered rocks.
Visitors need to trek deep into the forest to visit Hung Thoong.
The deeper you go, the slower your pace becomes, influenced by the terrain. Attention is no longer focused on the expansive landscape but on each step, each point of support. Without a stable surface long enough for the body to become accustomed to the path, everything constantly has to be adjusted.
When a sinkhole opens up, it creates a void with no way back.
The highlight of the journey is the sinkhole system – where the ground suddenly opens up into deep vertical caverns, leading down to the cave spaces below.
The moment of rappelling down into the sinkhole is the most tense part of the entire journey. Standing at the edge of the sinkhole, with a sheer vertical abyss below, the initial feeling is one of natural apprehension due to the depth and slippery rock surface. But as you begin to move according to the instructions, each movement gradually brings your body into control: hands gripping the rope, feet finding handholds, body weight adjusted in rhythm with the descent.
The entire process of rappelling down the sinkhole is considered part of a challenge-based adventure, where participants must constantly adjust their bodies to adapt to the height, cliffs, and safety ropes throughout the descent.
Three days amidst caves, waterfalls, and the limits of the body.
Beyond the sinkhole, the journey includes many other experiences. Ziplining gives the sensation of lifting the body off the ground, the speed pulling you through the forest in a matter of seconds. Swimming in the cave transports participants to another world, where light fades, cold water surrounds them, and limestone walls close in like a natural corridor stretching for thousands of years.
At Lake Mada, climbing waterfalls and jumping off cliffs requires decisive action in a short amount of time; there's no time for deliberation, only action and reflexes.
Between those activities were very real breaks: meals in the forest were fully prepared, not feeling makeshift as many people imagine. According to Trinh Tu, the food on the tour was a pleasant surprise; from the main meals to the BBQ at the end of the trip, everything was carefully prepared, providing enough energy to sustain the intensity of activity for many consecutive days.
What makes this journey so highly regarded is not only the adventurous experience but also the way it's organized into small groups and ensures safety. Before each leg of the journey, equipment is checked. Ropes, harnesses, and anchoring systems all have dedicated personnel. Guides are positioned in various locations to ensure each person receives direct support when they begin moving. This allows participants to experience a genuine challenge without losing control.
At the end of the journey, what remains is not just the places visited, but the feeling that the body has lived in a completely different environment: more movement, greater focus, and a simpler life.
Hung Thoong is not a cave tour, but a series of experiences that force people to push beyond their physical limits, returning with a clearer understanding of themselves.
