The memorial in New York City at the site where the Twin Towers fell in the Sept. 11 attacks 15 years ago straddles two worlds: one of the living and one of the dead.

A marker for where more than 2,600 people were killed, attracts tourists from around the world. Some are drawn there to pause and reflect, others to satisfy a morbid fascination with the site of the worst attack on US soil since Pearl Harbor was bombed in 1941.

Clutching cell phones, cameras and selfie sticks, visitors usually take their time around the National September 11 Memorial Museum. They are expected to turn out on Sunday for the 9/11 anniversary.

More than 28 million people have seen the memorial and 7 million have been to the museum since they were opened five years ago, leaving some local people thinking the significance of the site is fading as it becomes just one more tourist site.

Rosanne Hughes' husband died on Sept. 11, 2001, while he was on a work visit at the Windows on the World restaurant high in the World Trade Center's North Tower.

Now a board member of the New Jersey 9/11 Memorial Foundation, Hughes said that it was hard for victims' relatives to sometimes see insensitive or even rude behavior at the plaza in Lower Manhattan.

Hughes said, "It's very disrespectful for people to go there and take selfies and smile for the cameras and in the background is where the towers collapsed. I saw people with their kids running around, you know laughing, having fun. I guess people just don't understand that it's just not that type of museum."

Early on the bright Tuesday morning in 2001, two hijacked planes were slammed into the North and South towers of the World Trade Center.

A third plane was flown into the Pentagon near Washington, D.C., and a fourth crashed in a Pennsylvania field.

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By Prakriti Neogi