The world's largest cave, Sơn Đoòng Cave, is featured on the new Google Doodle. It was a secret for years until its towering limestone walls were stumbled upon by a local farmer The Hang Son ...

The Hang Son Doong cave in Vietnam was a secret until the 1990s (Image: John Spies / Barcroft Media) Google is celebrating the discovery of the Sơn Đoòng Cave cave in its new Google Doodle .