How anyone could know precisely where to drive off a flat desert highway without the benefit of landmarks, or a GPS, to find a little known fort that is poorly depicted on maps and hidden in a wilderness of rock, was the question I kept turning in my head, as Ahmed al-Shalaan steered our vehicle tentatively off the asphalt. “I came this way once before, many years ago,” he said, smiling as though he had divined my thoughts.