(CNN) -- The crowds continue to visit the dead.
They walk through the gates at Auschwitz. They take the boats to the USS Arizona in Pearl Harbor. They hike through battlefields and slave auction sites.
And now they walk onto the plaza of the National September 11 Memorial, where the World Trade Center towers once stood. Already one of New York City's most popular attractions, the new memorial has drawn more than 2 million visitors since it opened on September 11, 2011.
In a culture where death is sanitized and often left to hospitals and hospice centers away from people's daily lives, death made public by tragedy fascinates people enough to make memorial sites a popular stopping point on otherwise fun-filled vacations.
Also known as thanatourism, dark tourism is travel to sites where death or suffering has occurred or been memorialized. These locations can include Holocaust sites, battlefields, prisons, slavery sites, graveyards and other places of great suffering.
It's become widespread and popular enough to support the new Institute for Dark Tourism Research at the University of Central Lancashire in England, which launches with a conference on Tuesday.
"Throughout history, we have always held an inherent fascination with death and our mortality," said Philip Stone, senior lecturer at the University of Central Lancashire and founder of the institute.
"Dark tourism in its various shades can potentially provide individuals in contemporary secular societies a vehicle to get up close and personal to tragic events that have perturbed our collective consciousness," said Stone.
"Dark tourism simply provides a modern means in which the death of others can be consumed at a distance and in safe and socially sanctioned environments. This, combined with increasing academic and media spotlights on the commercialization of death, is why dark tourism might be so popular."
Tourists' fascination with death is nothing new. For millennia, people have retraced the pilgrimages of religious saints and other iconic spiritual figures who sacrificed their lives for their faith. And where ancient Romans once cheered gladiators battling to the death, tourists now visit the ancient Roman Coliseum. Where crowds once gathered to watch the Salem witch trials, tourists now go to learn why women were condemned to die.
Why people visit the dead
It's not hard to understand why people visit the National September 11 Memorial in New York City. Many people can still clearly remember that day. When a shared tragedy is still present in the public consciousness, people want to do something with those feelings, say experts.
Because September 11 "was a shared global moment, there is a natural and strong desire to come to where those events took place," said Joe Daniels, president of the memorial and planned museum. "People remember the towers, the day when the towers came down, the recovery period, and the empty pit. People really want to be part of history and want to come to this place."
When memories of the actual events fade, many people still come to memorials looking for answers as to why an awful thing could happen: How could Adolf Hitler have perpetrated the Holocaust? Why did Cambodia's Khmer Rouge murder its people? Why did Japan attack the United States at Pearl Harbor?
It's a balancing act for memorial sites: How to teach the cruel facts of tragedy to an audience that is often on vacation. National Park Service staff at Pearl Harbor welcome over 1.5 million visitors annually to the USS Arizona, often as part of a more festive trip to Hawaii. The park service shows a film to set the tone before visitors board U.S. Navy boats to visit the site of the damaged vessels.
"Ultimately, visitors come to our sites, to memorials, to remind themselves of some larger human value that transcends the petty parts of our day-to-day lives," said Paul DePrey, superintendent of the World War II Valor in the Pacific National Monument at Pearl Harbor, which includes the USS Arizona, USS Oklahoma and the USS Utah Memorials.
"Visits to memorials remind us of ideals that are always on the periphery of our awareness, but shape our values: sacrifice for others (USS Arizona Memorial), courage in the face of danger (Flight 93), speaking truth to power (Martin Luther King, Jr.), tenaciously clinging to hope in spite of constant terror (Holocaust Museum)."
"The people who are memorialized are the unlucky ones," DePrey said via e-mail. "They died without choice. Those of us who live on have a responsibility to ensure that the reasons for those deaths are not swept under the rug of inconvenient history. We identify the need to acknowledge that something terrible happened in our history. Memorials remind us not just of who the heroes are, but why we consider them heroes."
Who decides a memorial's message?
What answers people get about who died and why, depend on who controls the memorial's message. People visiting the Auschwitz-Birkenau Memorial and Museum in the 1980s when Poland was controlled by the Soviet Union would have heard primarily about the deaths of Polish Catholics there, according to Daniel Eisenstadt, co-founder of the Auschwitz Jewish Center Foundation, which represents the lives of the pre-war local Jewish community.
With more freedom to discuss the history of the camps, Auschwitz evolved into a more historically accurate account to include the Jews as Auschwitz's primary victims and other details of the mass murder.
That passage of time allows memorials and museums built amid fierce political debate to include other views. As gay people started fighting for their civil rights and gay issues rose to the forefront of the national debate, Holocaust memorial museums responded to demands that gay victims of the Holocaust be included in the accounting of the victims by including references in their exhibitions.
The fight by African-American descendants of slaves to make sure slavery is fully represented in history has also changed the way Southern memorials are presented. Historians and descendants of free and slave families who lived and worked on Southern plantations, along with emerging archaeological and historical records, are helping to tell a more complete story at South Carolina's historical sites, including Redcliffe Plantation State Historic Site in Beech Island, said Dawn Dawson-House, spokeswoman for the South Carolina Department of Parks, Recreation and Tourism.
"Redcliffe was once described as the former home of South Carolina Gov. James Henry Hammond, who supported South Carolina's secession and was widely known as the statesman who yelled 'Cotton is King' during a session of the U.S. Senate," said Dawson-House. "It's now interpreted as the governor's home, the home of three generations of his descendants and numerous African-American families like the Henleys, Goodwins and Wigfalls who worked at the site as slaves and later free men and women."
Enforcing appropriate behavior
As time passes and people who lived through a tragedy aren't around to remind viewers of their losses and enforce decorum, it can get harder for memorial staff to enforce appropriate behavior at sites honoring the dead.
Visitors to the Pearl Harbor memorials are asked to maintain a respectful atmosphere. The 1.4 million annual visitors to Auschwitz are expected to behave with "appropriate solemnity and respect" and follow a series of other rules designed to protect the reputation of the site's victims and the grounds.
"The site demands respect," said Paweł Sawicki, a spokesman for Auschwitz. "When you walk in the authentic area with the fences, watchtowers visible, when you see the ruins of gas chambers, or prisoner barracks, you generally do not act disrespectful. That seems to be the huge power of authenticity."
Yet time can dull the sense of tragedy. Two cruises organized to commemorate the ill-fated Titanic journey had their solemn moments of memorial, but there was also lots of dining and fun scheduled during those trips. And perhaps the people heading to Nova Scotia to visit the Maritime Museum of the Atlantic and cemeteries filled with the Titanic dead can be forgiven for confusing fact with fiction. Dublin-born Joseph Dawson, 23, worked on board and was buried at Fairview Lawn Cemetery in Halifax. His tombstone gets flowers brought by fans of Jack Dawson, the character played by Leonardo DiCaprio.
(Whatever draws visitors, organizers of Nova Scotia events marking the recent 100th anniversary say their respectful tributes to the Titanic tragedy and the permanent collection of Titanic artifacts help educate visitors about the real loss of life that day.)
And certainly the culture of a particular place can take over. New York City is known as the city that never sleeps, and business certainly doesn't. It didn't take long after the World Trade Center fires were put out for small-time vendors to sell mass-produced $5 T-shirts and photos of the heroics at ground zero.
While some of that selling still goes on around the site, maintaining a tone of respect is much easier now that the memorial is built, said Daniels, the memorial president. "It's almost impossible for someone to step onto Memorial Plaza and not have a sense of their breath being taken away."
Daniels knows future generation won't have the intense memories of September 11 that makes the memorial all the more powerful. "That makes our job even more important, when people don't have a direct connection," he said.
"It's our responsibility to make people understand what happened on this site, not just the tragic parts, but the coming together aspects. That goes to the second prong of our mission: building a museum that will deeply explore 9/11 -- a place where people can come and learn."
A new focus on life
When lawyer Daniel Eisenstadt visited Auschwitz many years ago, he was struck by the anonymity of the Jews who died there. To him, Auschwitz was "the ultimate posthumous victory for Adolf Hitler," he said. "All the people visiting knew about the people who were killed was the anonymity of the people who were killed. It was very much in line with Hitler's basic line about the Jews."
Eisenstadt and friend Fred Schwartz wanted to focus on the lives of the people who died. Their wish to provide context for the rich and diverse Polish Catholic and Jewish pre-war community surrounding the camps turned into the Auschwitz Jewish Center Foundation, which opened in 2000 in a renovated former synagogue in the old city center of Oświęcim, a few kilometers from the camp.
Now a subsidiary of the Museum of Jewish Heritage in New York, the center educates international visitors, Polish school children and even visiting U.S. military officers studying genocide about the rich life of the Jewish community beyond the genocide.
"There is a trend in memorials to incorporate life itself, not just how people were killed but how they lived," said Eisenstadt, who served as the center's first executive director for three years and is now a board member.
That's also happening at the September 11 Memorial, according to Daniels. He's glad that people celebrate New York with a Broadway show and visit to the Statue of Liberty along with a visit to the memorial. Even as people pay tribute to the victims of 9/11, New York is thriving in and around the 16-acre site where the towers once stood.
"When you step on the memorial on the eight acres where the towers once stood, there are eight other acres where other buildings are being built," said Daniels. "Other commercial buildings are rising up around you. There is rebirth and moving forward."
What memorial sites have you visited and why did you go? Please share your experiences in the comments section below.