Then she noticed something in the rockface reflecting the sun's rays and, on closer inspection, realized it was actually a window.

The dome was lined with thousands of tiny mother-of-pearl tiles, which reflected the sun onto the worshippers in a spray of rainbow light.

Looks like a mirror only, of course, it's not a mirror, it's a U-boat's periscope reflecting the sun.

Yet the sun was reflected, whitely, strangely, from myriad surfaces, as if the lush green of May was mostly moisture, and ephemeral.