May 21, 2026, 8:22 am | Read time: 4 minutes
Near the Chinese city-province of Chongqing lies a natural wonder of truly epic proportions. The Xiaozhai Tiankeng is the deepest sinkhole in the world, so deep that skyscrapers would disappear into it. But what is truly astonishing is the unique ecosystem that has formed at the bottom of this abyssal doline. It seems to follow its own set of rules.
In southwest China, near the metropolis and city-province of Chongqing, lies perhaps the greatest natural wonder of this vast country. And that is meant literally, because among sandstone formations shaped by nature over millions of years yawns the Xiaozhai Tiankeng, the deepest sinkhole in the world. More than half a kilometer deep and almost as wide, the earth opens up here in a dizzying chasm. Sunlight rarely reaches the bottom of this crater. Yet a unique ecosystem has developed here, unmatched anywhere else in the world.
But let’s start at the beginning. A sinkhole, also known as a doline, forms when an underground cavity collapses due to erosion. In the case of the Xiaozhai Tiankeng, this process likely took tens of thousands of years, according to the BBC. Rainwater steadily eroded the porous sandstone, while a powerful underground river carved out massive caves and cavities. Then, suddenly, the ground collapsed, creating the enormous hole. Its dimensions are truly gigantic. It is 626 meters deep and 527 meters wide. That’s enough space to fit the Eiffel Tower twice or fill 40,000 Olympic swimming pools with water.
The Flora Works Differently Here
Scientists have long been fascinated not only by the dimensions of the Xiaozhai Tiankeng but also by the unique ecosystem that has developed at its base. It’s a different world, like something out of a fantasy film, where researchers described more than 1,200 plant species in a 2024 study in the Chinese Journal of Plant Ecology. They examined 64 of them and discovered something astonishing. The flora in the world’s deepest doline actually “functions” differently than comparable systems on the surface. The authors write in their study, among other things: “The leaves of the plants (…) contain less carbon but higher amounts of nitrogen, phosphorus, and other nutrients.”
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Specifically, this means that the flora in the Xiaozhai Tiankeng is far less frugal with the nutrients available to it than its counterparts growing elsewhere. As a result, the plants in the sinkhole grow much faster than usual. The conditions they find here are more constant than in other places due to the unique location. The temperature is relatively stable, there is high humidity, and little direct sunlight. Scientists observed various survival tactics among the plants. Some even altered their leaf structures to better adapt to the available light conditions.
Discovered Only in 1994
Additionally, the soil in the Xiaozhai Tiankeng creates the special growth conditions that prevail here. Depending on the location studied, the nutrient composition in the soil varied significantly. This directly affects the nutrition of individual species as well as entire plant groups. It is a microcosm that operates by its own rules. Due to the steep walls, the forest at the bottom of the world’s deepest sinkhole is isolated from the ecosystems on the surface. The name of the place is a combination of two terms. Xiaozhai is an abandoned village in the area, and Tiankeng means “Heavenly Pit.”
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Incidentally, the Xiaozhai Tiankeng was “discovered” only in 1994, according to the BBC. Locals had known about it for centuries, but it was then that a British team of speleologists first attempted to map the massive chasm. An effort that failed five times over ten years. The researchers simply did not dare to navigate larger sections of the still-flowing underground river. Thus, the world’s deepest sinkhole remains a world that likely holds more secrets than it has revealed so far.