Missionary Hears Echo Inside Crevice, Learns Its Actually a Sprawling Cave 5.6 Miles Long

Entrance to Jeita Grotto, in Lebanon (AlexelA/Shutterstock); (Inset) The upper galleries of Jeita Grotto. kcakduman/CC BY 2.0

The gunshot fired by an American missionary marked the discovery of a national treasure deep underground.

In 1836, while exploring the Nahr El-Kalb River valley about 11 miles north of Beirut, Lebanon, the missionary William Thompson saw a trickle of water flowing from a fissure in the rocks and he set about investigating.