EAST GRANBY, Conn. — Entering the mine at Old New-Gate Prison & Copper Mine is like being hit with a burst of air conditioning.

A staircase leads to a tunnel more than 30 feet below the earth's surface and winds its way through the darkness, where the air is a constant, chilly 52 degrees.

"Cool, what's over there?" said 8-year-old Elijah Baker, his sandals slapping the wet basalt, where moisture seeps down from the ground above and slithers along the rocks.

The tunnels seem to go on forever in what is considered the birthplace of the American copper industry. Old New-Gate Prison & Copper Mine offers a glimpse into a colonial-era industrial wonder, carved out long before there was dynamite, big drills or open pits.

About 30 minutes north of Hartford, Connecticut's capital city, it's not only the nation's first chartered copper mine but also the country's first state prison, a place that once housed criminals and British loyalists during the Revolutionary War.

COPPER FOR CANNONS

Even its history as a tourist attraction is more than a century old. It was opened to curious visitors in the mid-1860s. Today it is a national historic landmark.

The mine, established in the early 1700s, consists of about two miles of tunnels, said Lance Kozikowski, the site supervisor. Much of the copper excavated from the site was moved along the Connecticut River and up to Boston, where it was shipped to refineries in England. The red metal was used for many items during that period, from coins to cooking utensils to cannon barrels. Today, copper is used in everything from the electrical wiring in homes to car motors.

The mine in East Granby didn't generate enough profit and was shut down around 1770 after nearly 70 years of excavation. But as the mine was going under, copper mines began cropping up across the country. Eventually, much larger copper deposits were found in states such as Arizona, Utah, New Mexico and Michigan.

"By the time you hit the mid-1800s, all the activity was focused on the Midwest," said Ken Geremia, communications coordinator for the Copper Development Association. "It was a far more efficient and cost-effective area to excavate and mine the copper."

MINE BECOMES PRISON

Geremia estimates about 100 small copper mines and dozens of larger ones operate around the country, making the United States the second-leading producer of copper behind Chile.

Down in the tunnels, remnants of copper ore are everywhere.

"Oh, there's copper on the ground right there," said 9-year-old Joshua Baker, pointing out the greenish tinge in a rock to his cousins Elijah and 7-year-old Isaac, who live in Farmington.

The three bent down to look.

Their grandmother, 59-year-old Jan Baker, walked behind, following the racing echoes of their voices through the tunnels.

"Helloooo," Isaac shouted. He stopped to look up a 45-foot hole, part of a well that provided water to the inmates. The well, now filled with gravel, harkens back to the second use of the mine as a prison. The prison well once claimed the life of an inmate, Abel Starkey, who tried to escape with a rope thrown down by a prison guard who had been bribed, Kozikowski said. The rope snapped and Starkey fell to his death.

There were many attempted escapes in the nearly 50-year history of the prison. When it opened in 1773, John Hinson became the first to enter New-Gate and the first to escape. With the help of a conspirator, the convicted burglar climbed a 70-foot shaft to find his way out after just 18 days. In the early days of the prison, miners, not guards, were in charge of the prisoners.

"It was a good idea but unfortunately, like most criminals, they're going to want to get a way out, and these miners were not guards, they were not armed and, as a result, the prisoners would bang them over the head with a shovel and try to escape," Kozikowski said.

As criminal activity increased in the colonies, the need for a place to incarcerate criminals grew, Kozikowski said. At the time, the mine seemed ideal. It was isolated and the prisoners could sleep there and also generate income by working the mines. But by the turn of the century, copper mining had ceased to be fruitful and the prison turned to making nails that were sold to the general public, Kozikowski said. Inmates also produced whiskey barrels for a distiller down the road, fashioned wagon wheels as farming in the area burgeoned, and made shoes.

SEEING EARLY HISTORY

At any given time, there were 90 to 100 inmates at the prison, Kozikowski said.

By 1800, the prison had built its first cell block above ground in an effort to provide more humane living conditions.

In 1827, the prisoners were transferred to the newly constructed Wethersfield State Prison, a larger prison closer to the capital.

"Why do people come?" Kozikowski said. "They don't come to see a pile of rock in ruin. Some people are students of history and penology, and they want to know about the early prisons and how they came about and how the prisoners were treated, but the vast majority of people, the first place they head to are the copper mines.

"It's unique," he added. "Where else in New England can you visit a copper mine underground? Nowhere. This is it."