The Economic Times

In 1990, a Vietnamese farmer hiding from storm found a 655-feet-high cave where clouds formed above an underground river while a collapsed roof let in sunlight that fed a 165-feet tall forest

A Vietnamese farmer stumbled onto Hang Son Doong in 1990 while sheltering from a storm, though the cave's true scale was only confirmed after British cavers surveyed it in 2009. Guinness World Records lists it as the world's largest known single cave passage, holding a forest of trees up to 165 feet tall fed by sunlight through a collapsed roof, along with an underground river that creates mist and clouds inside.