Where is the world's largest known cave chamber made by an animal?

The Great Barrier Reef lies in the Coral Sea off the northeastern coast of Queensland, Australia. It is not a single organism, but the world’s largest living structure made by animals—tiny coral polyps that build massive limestone formations. The reef stretches for more than 2,300 kilometers and includes thousands of reefs and islands. It supports extraordinary biodiversity, from fish and sharks to turtles and seabirds. Because it is living and constantly changing, it is often described as one of Earth’s greatest natural wonders.