In tourist brochures and online, there is nothing to suggest that “Cave 8” at the Shizhonghshan Grottoes (石钟山石窟) of Jianchuan county, Yunnan province, holds anything scandalous. Most of the sightseers here, high in the mountains above the rapidly touristifying town of Shaxi, walk straight through the site with glazed eyes, distracted by the view or the perilous hijinks of their small children atop the cliff edge. It’s the last cave of the collection, so they think they know what to expect—more statues of the Buddha, forgotten local kings, and poems in spidery scripts.

All the more surprising when Cave 8 hits you square between the eyes, the last thing you’d expect to find in a Buddhist holy site: In a niche flanked by bodhisattva statues and bedecked with lotus flowers, a stone sculpture of a vagina the size of a watermelon stands proud atop a plinth.

Signs introduce the carving as the Ayangbai (阿姎白) and urges scholars and visitors to “engage in debate” as to what this bizarre sculpture could mean and how it got into this unlikely spot. This is because little is known about it; even the meaning of its name is disputed. The sculpture is a curious anomaly in this cave complex built between 850 and 1179, itself filled with statues of the rulers of the Dali Kingdom, whose independent territory stretched across most of present-day Yunnan until it was subsumed into the Mongol Yuan empire in 1253.

“There is no consensus on Ayangbai, only various theories,” Dong Zengxu, president of the Jianchuan County Cultural Heritage Research Institute, tells TWOC. “But we know one thing—the practice of worship toward Ayangbai for fertility and reproduction has existed among the local people from ancient times to the present day.”

Scholars have suggested the name Ayangbai may be a corrupted transliteration from the languages of the Bai ethnic group living down on the Shaxi plain, or the Yi people of the surrounding mountains. As bai is the Yi word for female genitalia, some try to link the word to the Yi language, while scholars of the Bai people claim the word was originally a Bai euphemism: “little child door.”

When and why Ayangbai was created is also unknown. Perhaps it wasn’t meant to be there at all. The first study of the grotto, made in 1951 for China’s Ministry of Culture, pointed to the roughness of the carving compared to the finely-hewn figurines surrounding it, and concluded the Ayangbai was added after the original grotto was finished. According to the theory, there was originally a figurine of a goddess—possibly the Guanyin bodhisattva—atop the lotus seat, but a single crack developed in the statue, and it was retouched over the centuries into genitalia that became the object of fertility rituals.

Or maybe the vagina was there first: In a 2014 paper, Zhu Wenxu of the Minzu University of China argued that Yi people from mountainous areas performed fertility rituals across several natural locations in Yunnan province. This site was one of them, Zhu believes, and the primitive totem was later integrated into a site of Buddhist ceremony, allowing old and new religions to coexist together.