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The Chernobyl Nuclear Power Plant in Ukraine. On April 26, 1986, an explosion and fire at the plant released massive quantities of radioactive material into the air. Hundreds of thousands of people fled their homes, and the nearby town of Pripyat remains an eerie ghost town to this day.
A woman cries during a remembrance ceremony at the memorial to the victims of the Chernobyl Nuclear Power Plant in Kiev, Ukraine.
Omaha Beach was one of the principal landing points for Allied Soldiers during the Normandy invasion in World War II. At the top of the bluff overlooking the beach is the Normandy American Cemetery and Memorial for the soldiers killed in the invasion.
A cannon stands at Gettysburg, the largest Civil War battlefield site in America. The battle was the Civil War's bloodiest, with 51,000 casualties. President Lincoln later consecrated the site as a national cemetery with his historic Gettysburg Address.
The USS Arizona Memorial at Pearl Harbor in Honolulu. In all, 1,102 sailors were killed on the ship during the attack on December 7, 1941, by Japanese imperial forces.
The eternal flame at the Tomb of the Unknown Soldier at the Arc de Triomphe in Paris. The flame burns in memory of all the unidentified soldiers who fought and died for France in both the first and second world wars.
On April 16, 2007, 23-year-old Seung-Hui Cho shot and killed 32 people in 2 separate attacks on the Virginia Tech campus. Today, 32 pieces of stone now lie at the Drillfield viewing stand to commemorate the victims of the single deadliest shooting incident by a single gunman in US history.
The Tuol Sleng Genocide Museum commemorates those who perished in the infamous killing fields of Cambodia. The museum houses the skulls of people killed and buried by the Khmer Rouge regime during its rule from 1975 to 1979.
Endless rows of military graves at Arlington National Cemetery in Virginia. Veterans and military casualties from each of America's wars are interred at the cemetery, from the American Revolutionary War to the current conflicts in Afghanistan and Iraq.
The Srebrenica Genocide Stone -- a memorial to the 8,000 Bosniaks (Bosnian Muslims) murdered in Bosnia and Herzegovina by the Army of Republika Srpska in July 1995.
The entrance of the Auschwitz-Birkenau concentration camp in today's Oswiecim, Poland, where an estimated 1.1 million people were killed.
The Gates of Time at the Oklahoma City National Memorial. On the western gate, '9:03' represents the moment after Timothy McVeigh detonated a bomb that killed 168 people.
The Flame of Hiroshima and Nagasaki at the Ueno Toshogu Shrine in Ueno Park, Tokyo. Hundreds of thousands of people were killed when the US dropped atomic bombs on the 2 cities in August 1945. The flame will burn until all nuclear weapons are abolished.
With two fountains, the memorial commemorates the September 11 attacks of 2001, which killed 2,507 civilians, 72 law enforcement officers, 343 firefighters, and 55 military personnel, and the World Trade Center bombing of 1993 which killed six civilians.
The Pentagon Memorial. Each of 184 benches at the memorial represents someone killed during the 9/11 attacks. Benches facing the Pentagon represent someone killed inside the building; benches facing away represent someone killed on the plane.