Deep in central Vietnam, near the Laos border, a giant cave hides an ancient “world” beneath its surface, home to an entire ecosystem. Known as Hang Son Doong, this vast underground cavern is so big that it supports its own weather system and houses a flourishing rainforest.
Recognized by Guinness World Records in 2013 as the largest cave on Earth, it has since become one of the most extraordinary natural wonders ever discovered. It stretches over four miles in length and measures up to 2,149 feet high and 1,608 feet wide.
The cave’s volume is estimated at more than 414 million cubic feet—large enough to accommodate a city block of skyscrapers. Inside, mist rises from an underground river, forming clouds beneath the cave ceiling, a phenomenon rarely seen in such environments.
Openings in the ceiling allow sunlight to reach a forest inside
Parts of its ceiling collapsed hundreds of thousands of years ago, creating massive openings known as dolines. These natural skylights allow sunlight to stream in, fueling the growth of dense vegetation.
As a result, a tropical forest thrives within the cave, complete with towering trees and other unique flora. Two additional skylights, along a 984-foot-wide fault line, further illuminate the chamber, allowing even more light to reach the forest floor.
Hang Son Doong, the world’s largest known natural cave in 🇻🇳 Vietnam.
The main passage is more than 5 km (3.1 mi) long, 200 m (660 ft) high and 150 m (490 ft) wide.
(📸: Andrew Svk) pic.twitter.com/CrNppKFcTC
— Geography Host (@geographyhost) June 26, 2025
Formed over millions of years by the flow of the Khe Ry and Rao Thuong rivers, the cave’s limestone walls are estimated to be around three million years old.
Stalagmites and stalactites dominate the landscape, including a 967-foot calcite wall famously referred to as the Great Wall of Vietnam.
The cave was first discovered by a local man seeking shelter
Local man Ho Khanh first encountered the cave in 1990 while searching for agarwood in the jungle. As a storm hit, he took shelter under a cliff and noticed a strong gust of cold air and fog escaping from a nearby opening.
Though unsettled by the experience, the image stayed with him. It wasn’t until 2007, during an expedition in the Hang En area with British cave researcher Howard Limbert, that Khanh shared his story. Intrigued, the team followed his lead, and in 2009, they successfully relocated the hidden entrance.
The discovery drew international attention. According to Limbert, it was immediately clear they had found something unprecedented—an untouched natural system on a scale no one had imagined.
Access is limited, and physical fitness is required
Despite its global fame, access to Hang Son Doong remains tightly controlled. Only one operator, Oxalis, is licensed to lead tours, and the experience is not for the average traveler.
Participants must be between 18 and 70 years old, physically fit, and able to complete five-mile treks with 984 feet of elevation gain. They must also run 3.1 miles in under 50 minutes and climb five flights of stairs without exhaustion.
The five-day expedition includes jungle hikes, river crossings, rock scrambles, and rope climbs. Highlights inside the cave include formations such as the Hand of Dog stalagmite and the doline known as “Watch Out for Dinosaurs”. The route also passes through areas used as filming locations for the movies Pan and Neverland.
The journey, though demanding, offers a rare opportunity to witness a world unlike any other—one hidden beneath the surface of a giant cave in Vietnam.
