Theses caves, slowly carved out by an underground river over 90 million years, have been explored and excavated since 1938. A visit here (over 3km in length) begins with the Grave, a huge chasm 60m deep and 100m in length, which is attractively illuminated by a ray of natural light. This is the only cave with any contact with the open air (note the trees visible through the opening, which appear incredibly small). The highlight of the visit is the glistening White Cave, with its alabaster formations.