Th Right Blue, a diving and undersea photography blog, has a fantastic story about diving in Sipadan Cave off of Borneo. Jacques Costeau dove here in the 1980s and discovered an underwater cave filled with sea turtle bones. Much like the deep sea, underwater caves are dangerous, dark environments with its own unique ecosystem.
“While Cousteau and his group conjectured that old or sick turtles may have gone there intentionally to die, our guide told us that Cousteau’s original notion had been replaced more recently by a more prosaic explanation:”
(You have to go there to find out more!)