The Caverns of the Hidden One were a system of caverns deep below the surface of the planet Dorin. They were home to the Hidden Ones, a secret sect of the Baran Do—a Force-based organization on Dorin—dedicated to preserving the order's knowledge.
The caverns were first found and expanded by the male Kel Dor Baran Do Master Tokra Hazz, shortly after the Great Jedi Purge. Hazz feared that the Sages would be purged by the new Empire like the Jedi Order, and so secretly founded the Hidden Ones, a secret sect of the Baran Do dedicated to preserving the knowledge of the Order, so that, if the Baran Do ever were destroyed, the Order could be reinstated. He became the sect's first leader, known as the Hidden One, and probably created the tradition of the dying ceremony as a means of joining the sect.
In 43.5 ABY the recently exiled Jedi Grand Master Luke Skywalker and his son, Jedi Knight Ben Skywalker, arrived on Dorin, seeking to speak with Baran Do Master of the Order Koro Ziil. They eventually traveled to the Caverns of the Hidden One, and, after Luke dueled with Koro Ziil, convinced the Hidden Ones to leave the caverns and return to the surface.