BENSON, Ariz. (AP) _ The outside retreats the moment you start down the cut limestone tunnel leading to the Kartchner Caverns' wondrous depths.

Light and heat give way to deepening shadows and a cooling dampness as the first of two stainless steel airlocks clangs shut.

Step through the second airlock, and you're greeted by a chamber with walls climbing almost four stories to a ceiling peppered with tawny and chocolate-colored stalactites. Stalagmites jut like needle-tipped spears from the floor in the Rotunda Room 40 feet below ground.

This room, these caverns, stood untouched for hundreds of thousands of years until discovered 25 years ago by two spelunkers, who then kept them a secret for four more years to ensure their preservation.

After much fanfare, anticipation and relief following a two-year delay and cost overruns with the $28 million project, the public will get its first glimpse Nov. 12, when Kartchner Caverns State Park opens.

Some who already have viewed the 2 1/2-mile cave complex in the Whetstone Mountains, about an hour southeast of Tucson, are clearly smitten.

``There are beauties you cannot imagine,'' said Randy Tufts, who discovered the caverns along with Gary Tenen. ``I remember just staring intently at everything, as if it might go away.''

After her tour last week, Arizona Gov. Jane Hull called it ``a religious experience. ... I had no idea of the magnificence of it.''

Unlike bigger and better-known caves such as New Mexico's Carlsbad Caverns, these caverns are still mostly alive and evolving thanks to moisture that drips from the tips of stalactites.

``It's probably 90 percent still alive. The cave formations are still growing, where many of the caves in the Southwest have dried up over the last 10,000 or 15,000 years,'' said David Jagnow, conservation chairman of the National Speleological Society, who mapped the caverns' geology before development began.

At Carlsbad, probably 90 percent of the formations have dried out, turned white and stopped growing, Jagnow said.

Kartchner Caverns were formed over time by underground water cutting through Escabrosa limestone. Water, with mineral deposits such as calcium and iron, also has fashioned the intricate formations, from dainty white lace-like helictites to formations resembling pearls, popcorn, cotton and butterscotch.

Colors run from pinks to taffy to corals to reds to creams.

Tenen and Tufts first made it inside in 1974 through a cut in a sinkhole on the Whetstones' east side after feeling a draft and smelling bat droppings. They entered the Rotunda Room slithering on their bellies in the pitch darkness with only hard-hat lights to guide them.

For years, the two Tucson men clung to their finding with secrecy, worried that others would damage the delicate formations. They finally confided in the landowners, James and Lois Kartchner, who later approached state officials with Tufts and Tenen. Secrecy prevailed, and by 1988 legislators approved acquisition and development.

The care that Arizona officials have devoted to the project sets it apart.

``It has established new standards for how caves should be developed,'' Jagnow said.

Experts studied the cave for several years first, helping to determine baseline conditions. That, in turn, should allow adjustments to keep the cave's environment stable.

``This is a story of conservation and stewardship,'' said Kenneth Travous, state parks executive director.

That's where some of the latest technology comes in.

Kartchner's special low-heat halogen lighting and a misting system were installed to help keep heat down and humidity up. Computerized sensing devices will monitor humidity, temperature and carbon dioxide levels _ all to minimize the impact of hundreds of visitors a day because the caverns' formations, called speleothems, are so fragile.

Even oily skin deposits left behind by someone touching one of the formations could damage something that was thousands of years in the making. One state employee was charged with vandalism, sentenced to community service, fined $100, placed on probation for two years and fired for breaking a 6-inch-long stalactite estimated to be 1 million years old.

Visitors on the reservation-only tour will be accompanied by guides instructed to follow 1,800 feet of hand-poured concrete trails, which perhaps best illustrate the drastic changes in the caves since development began.

Travous estimates 150,000 to 200,000 people will visit in the first year _ the park's reservation system was swamped the moment it opened in August.

So far, the state has spent $28 million on the project, but Travous said that total is expected to top $30 million by the time two other major rooms and a few thousand more feet of trail are developed.

Some will likely say it was worth it.

``We have literally had people in tears at the end of the tour,'' Travous said. ``It's just a real nice experience.''