Atlas Obscura
Umm Jirsan Cave in Khaybar, Saudi Arabia
Located in the Harrat Khaybar lava field in Saudi Arabia, Umm Jirsan is a 1500-meter-long lava tube system, with tunnels that are as much as 12 meters tall and 45 meters wide, and is estimated to have been formed nearly 3 million years ago. Lava tubes form when cooling rivers of lava leave behind large openings in the earth's crust. It had previously been suspected that early humans might have…
Explored cave in 2009, found hundreds of thousands of bones