Somewhere below the surface of the kiddie-pool sized patch of brown water is the entrance to the 2,300-year-old tomb of a pharaoh named Nastasen. If I crane my neck back far enough, I can just make out the eastern flank of his pyramid rising nearly three stories above me.

It’s a sweltering morning in the desert of northern Sudan, the land of Nubia in the time of the pharaohs. Sweat drips into the dive mask hung around my neck as I negotiate my way down a narrow, ancient staircase cut deep into the bedrock. Waterproof flashlights clank from each wrist, and a 20-pound weight belt is slung commando-style across my chest. An emergency container of air, no bigger than a can