In eastern Yemen there is a hole in the ground known as the Well of Barhout, aka the "Well of Hell." Located in the Hadhramaut region, the hole is 30 meters wide and 112 meters deep. According to local reports, the Well of Hell is a prison for demons as indicated by the horrible stench emanating from it. Recently, explorers descended to the bottom of the hole for the first time. Unsurprisingly, the demons hid from the interlopers. From Phys.org:
"There were snakes, but they won't bother you unless you bother them," Mohammed al-Kindi, a geology professor at the German University of Technology in Oman, told AFP[…]
"Passion drove us to do this, and we felt that this is something that will reveal a new wonder and part of Yemeni history," said Kindi, who also owns a mining and petroleum consultancy firm.
"We collected samples of water, rocks, soil and some dead animals but have yet to have them analysed," he said, adding that a report will soon be made public.