JEFFERSON CITY, Missouri (Reuters) - Halfway through a tour of the bleak, deserted Missouri State Penitentiary - notorious in its day for assaults, murders and gas chamber executions - nurse Donna Springer tried to explain why she wanted to visit such a place.
"Well, it's like ... 'This could have happened to me,'" said Springer. "You have a fascination with it in some way."
Former prisons, complete with gift shops and paranormal components, have become increasingly popular tourist destinations in America and abroad. Playing to the public curiosity about life behind bars, more than 100 former prisons and jails have tours or museums, according to a list posted on the website of the Eastern State Penitentiary in Philadelphia.
Some, such as Eastern State and the Missouri prison, report steadily rising visitor numbers.
The 177-year-old Missouri penitentiary in Jefferson City is the biggest tourist draw in town, aside from the State Capitol building a few blocks away, tourism officials said.
"People are intrigued about what is behind those walls." said Diane Gillespie, executive director of the Jefferson City Convention & Visitors Bureau.
The Missouri penitentiary had more than 19,000 visitors last year, up 10 percent from the previous year. Visitors pay $12 for a two-hour tour and $25 for a three-hour, in-depth look that includes additional areas of the compound, once the largest in the United States. From 2009, the tours have provided a new use for the prison, which had an uncertain future when it closed in 2004.
Some other prisons in the U.S. also report a booming tourism business. Eastern State Penitentiary, with a "nighttime haunted house," draws about 160,000 people, up an average of 20 percent annually in recent years. The Old Idaho Penitentiary in Boise drew about 42,000 visitors last year, up from 28,000 four years earlier, officials said.
At Alcatraz - the most famous prison open for tours - the number of visitors to the island 1.5 miles offshore from San Francisco are capped at 1.4 to 1.5 million annually, said Howard Levitt, director of communications for the Golden Gate National Recreation Area.
"The demand far exceeds the availability of the tours," Levitt said. Alcatraz has offered tours since 1973 - 11 years longer than the 1934-1963 period when it was an active prison.
Prison tours cater to travelers interested in seeing the unusual, said Amber Beierle, visitor services coordinator for the Old Idaho Penitentiary.
"It's a place most of us would never in our lifetime see from personal experience," she said.
Some tours at the Missouri prison are given by former guards, who waste no time in calling attention to the brutal history of the place.
"Welcome to the bloodiest 47 acres in North America," said tour guide and former guard Bill Green, 65, his long gray hair flowing out from under a scruffy ball cap. "Men died within these walls by the hundreds - and not the low hundreds."
Time Magazine in the mid-1960s dubbed the prison the "bloodiest 47 acres" because of the number of inmates who killed or assaulted each other.
The prison housed the state's worst of offenders in crowded conditions. More than 5,000 inmates were crammed into the facility in the early 1930s, Green said. In 1954, prisoners rioted, burning down several buildings, killing four inmates and injuring guards and many other inmates.
Famous inmates at the Missouri penitentiary included gangster Charles "Pretty Boy" Floyd, heavyweight champ Sonny Liston - who learned to box while incarcerated - and James Earl Ray, who escaped in a bakery truck in 1967 and the following year assassinated civil rights leader Martin Luther King Jr.
Visitors can tour the oldest standing prison cell block, built in 1868, a four-story structure where cells are furnished with musty bunks and rusting toilets and sinks. A stop along the way is "the dungeon" - where inmates who broke rules were locked up in pitch dark, dirty conditions.
On Green's tour, his assistant Aloha Gerbes offers visitors a sobering directive: "Follow Bill. He will put you in one of the cells now."
The grounds of the prison include a former gas chamber, housed in a small limestone structure built by inmates in the early 1930s. Thirty-eight men and one woman were put to death there before the state changed its execution method in 1989 to lethal injection.
In the gas chamber, Green said, capital offenders suffered a "terrible death" by cyanide gas. "You don't just fall asleep," he told the tour group. "The cyanide rips out your sinuses, it tears out your esophagus."
Tourists can go inside the gas chamber and sit on the steel chair where prisoners were executed.
The goal of most prison tours is not solely to shock people but to show how the penal system has changed over the years. The Missouri tour also delves into work detail, where prisoners performed tasks such as making clothing, school furniture, license plates and many other items.
A big boost in prison visits has come from an interest in ghost or "paranormal" tours, officials said. Prisons are thought to be ghostly because they are cavernous, empty and have been the site of executions and other violent deaths, said Beierle at the Idaho prison.
But real prison stories are frightening enough to people such as Jim Rhiver, a retired minister who was on Green's recent tour.
"You can see how some people went in there for a very short time and still came out hardened," Rhiver said. "It was a terrible place to be."
Reporting By Kevin Murphy; Editing by Greg McCune and Gunna Dickson