"We realized we had a first-class cave"

Gary Tenen still makes regular visits to Kartchner Caverns — bringing bagels for the volunteers who help conduct tours. "I figure that's the only way they'll let me in," he jokes.

He'll never forget the "mixture of elation and disbelief" he felt in 1974 when he realized what he and his buddy, Randy Tufts, had stumbled onto.

"Randy and I had probably stuck our heads into hundreds of holes, maybe thousands," said Tenen, 55. "And pretty much my experience had been to crawl back into some dusty, rocky, crawl space that goes nowhere."

Tenen said he and Tufts, who died in 2002, were on their second exploration of the caverns before they got far enough inside to tell what lay in front of them. "It was on that second trip, when we discovered the Big Room, that we were just blown away, and we said, 'My God, this thing just keeps going.' That's when we realized we had a first-class cave."

Tenen, who runs a printing business in Tucson with his wife, said his favorite experience these days is to visit the caverns with schoolchildren and share his excitement, not just about the caves, but about science in general.

"What I try to convey is that sense of discovery. Whether it's a hole in the ground that gets you excited or that dark hole that's the eyepiece of a microscope or telescope. There's a lot to explore in this world."