It took time to learn a cave. When she finished mapping a section, it became like a good home, a place she knew intimately, yet still holding surprises. Her two favorite times to be in a cave were the first time-seeing everything new-and after she had mapped it and made it home.

A big cave like this one could take years to map. The landowners told her that no one had been through the entire cave. As far as she knew, she was the first to be in the section she was now in.

Diane took another drink of water. She listened for Mike, one of her caving partners, who should have been close behind her, but she didn’t hear him crawling through the tunnel.

She turned on her walkie-talkie. “Mike, the passage I just came through is tight.”

There was a moment of static before she heard his voice. “Guess I shouldn’t have eaten that pizza for breakfast.”

The section of zigzagging tunnels she’d just explored was devoid of any remarkable features but possessed a subtle beauty just from the color and texture of the rock.

Her gaze shifted again to the hole at the end of the tunnel. In another cave she’d crawled through a very similar hole that led into a cathedral room with flowstone draperies rippling across an entire wall, stalagmites that reached the ceiling like the trunks of giant redwood trees, and stalactites hanging like colossal chimes. Diane looked forward to getting to the hole at the tunnel’s end.

She took the bright yellow ultrasonic distometer from a pocket on her backpack to measure the tunnel length. The electronic device was more convenient than a tape measure-though she still carried a tape: There were some places that just had to be measured the traditional way.