She’d first glimpsed the cave in a grainy Cold War–era reconnaissance photo, its gaping entrance set high in a sheer rock wall resembling an ancient fortress. The picture had instantly captured her imagination. But what had planted the hook firmly in her imagination was the knowledge that no one had been able to set foot inside it. For 15 years, she’d obsessed over the same questions: How big was it? How deep did it go? What scientific treasures did it hold?