In March 2010, nine congregants of the Marrowbone Christian Brotherhood Mennonite Church were among eleven killed on Interstate 65 near Bowling Green and Mammoth Cave National Park in Kentucky's deadliest vehicle wreck in 20 years.
Renowned for his personal and experimental rigor, he conducted well-known sleep studies underground in Mammoth Cave, Kentucky and lesser-known studies underwater in submarines during WWII and above the Arctic Circle.
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Some other sources say it has about 133 miles (214 km) of surveyed passageways, making it the fourth-longest cave in the world, after Mammoth Cave, Jewel Cave and Sistema Ox Bel Ha.
Colossal Cave Adventure, a 1976 computer game based on Mammoth Cave National Park in Kentucky