Hang Son Doong is considered the biggest cave in Vietnam due to its immense size and volume. Measuring nearly 9 kilometres in length, it boasts sections over 200 metres high and 160 metres wide. The cave's volume is estimated at 38.5 million cubic metres, surpassing other caves in both size and grandeur. Its vast chambers, towering stalagmites, and unique ecosystem contribute to its distinction as the largest natural limestone cave in the world. The cave's discovery in 1990 by Ho Khanh and subsequent exploration in 2009 highlighted its unparalleled scale and geological significance.

Access to Hang Son Doong cave is exclusively through guided expeditions operated by Oxalis Adventure, the sole authorised tour provider. These tours are available from January to August, avoiding the monsoon season. The expedition includes a multi-day trek through Phong Nha Ke Bang National Park, with overnight camping inside the cave. Due to the cave's protected status and the challenging terrain, independent visits are not permitted. Booking in advance is essential, as only a limited number of permits are issued annually to preserve the cave's integrity and minimise environmental impact.

The Hang Son Doong cave expedition is priced at approximately $3,000 per person. This fee covers all aspects of the tour, including transportation from Dong Hoi, meals, camping equipment, safety gear, and the expertise of guides and porters. The cost also contributes to conservation efforts and permits required to access the cave. While the price may seem steep, it reflects the exclusive nature of the experience and the resources needed to ensure safety and environmental preservation during the expedition.

For the Hang Son Doong cave expedition, packing light yet appropriately is crucial. Essentials include sturdy trekking boots, lightweight clothing suitable for both warm and cool conditions, a waterproof jacket, and personal items like a headlamp and insect repellent. Oxalis Adventure provides camping gear, including tents and sleeping bags. It's advisable to bring personal medications, a camera, and a reusable water bottle. Given the cave's humid environment, moisture-wicking fabrics and quick-dry materials are recommended to ensure comfort during the multi-day trek.

The Hang Son Doong cave expedition is rated as a level 6 out of 6 in terms of difficulty, making it unsuitable for beginners. Participants should have prior trekking experience and be in excellent physical condition. The journey involves steep ascents, river crossings, and extended periods of hiking through rugged terrain. It's essential to assess your fitness level and consult with the tour provider to determine if the expedition aligns with your capabilities. Safety is paramount, and the challenging nature of the trek requires proper preparation and commitment.

Inside Hang Son Doong cave, a unique ecosystem thrives, hosting species adapted to the cave's dark and humid environment. Notably, biologists have discovered over 200 plant species, including mosses, vines, and trees reaching up to 30 metres in height. The cave's fauna includes rare and previously unknown species such as blind fish, translucent millipedes, and cave-dwelling scorpions. These discoveries underscore the cave's ecological significance and the importance of preserving its delicate environment for future research and conservation efforts.

Photography is permitted inside Hang Son Doong cave, and the stunning landscapes offer ample opportunities for memorable shots. However, participants are advised to use equipment that won't disturb the cave's natural environment. Flash photography should be used sparingly to avoid disturbing wildlife, and tripods may be restricted in certain areas to prevent damage to formations. It's essential to follow the guidance of the tour guides regarding photography practices to ensure the preservation of the cave's pristine condition.

The Hang Son Doong cave expedition is generally open to adults aged 18 and above. While there isn't a strict upper age limit, participants must meet the physical fitness requirements set by Oxalis Adventure. Those with pre-existing health conditions or concerns should consult with a medical professional before booking. The challenging nature of the trek necessitates a certain level of endurance and agility, so it's crucial to assess individual capabilities to ensure safety throughout the journey.

The optimal time to undertake the Hang Son Doong cave expedition is during the dry season, from January to August. This period offers more stable weather conditions, reducing the risk of flooding and making the trekking routes more accessible. The monsoon season, typically from September to December, brings heavy rainfall, which can lead to hazardous conditions inside the cave and surrounding areas. Planning your visit during the dry season ensures a safer and more enjoyable experience.

Hang Son Doong cave holds both geological and cultural significance. Geologically, it is the largest natural limestone cave in the world, with a volume of 38.5 million cubic metres. Its formation over millions of years has resulted in unique features like massive stalagmites, an underground river, and a thriving ecosystem. Culturally, the cave is a testament to the rich natural heritage of Vietnam and plays a vital role in local tourism and conservation efforts, providing economic benefits to the surrounding communities through responsible eco-tourism.

To preserve the delicate environment of Hang Son Doong cave, only a limited number of visitors are permitted each year. Approximately 1,000 tourists are allowed to participate in the expedition annually. This restriction helps minimise human impact on the cave's ecosystem and ensures that each visitor can experience its grandeur without compromising its integrity. Early booking is essential due to the high demand and limited availability of permits.

The "Great Wall of Vietnam" is a towering calcite formation located within Hang Son Doong cave. Standing at approximately 90 metres high, it is one of the cave's most striking features. This natural structure was formed over millions of years through the deposition of minerals from dripping water. The formation's sheer size and unique appearance have captivated explorers and visitors alike, making it a highlight of the expedition and a testament to the cave's geological wonders.