In the immediate aftermath of 9/11, NYC lost $323.7 million in tourism revenue as visitors scared of another attack left Times Square an empty shell of the soulless shell it usually is. But last year, the city's tourism industry had rebounded so much that it was expected to hit a record number. As it turns out, we exceeded those expectations: more than 48.8 million people visited NYC last year, spending $31.4 billion on our hot dogs, subways and hugs. And a shadow industry of 9/11 tourism seems to have grown out of that as a result.

As the Wall Street Journal points out, tourists can spend $59.99 for the NYC Freedom Tour, or $10 for a walking tour of Lower Manhattan led by someone personally affected by the attacks, or $20 for a tour of the Tribute WTC Visitor Center. There's even a name for this kinda of tourism, according to New York University professor Barbara Kirshenblatt-Gimblett: "dark tourism."

"The assumption fundamentally with tourism is that it's about escape, fun, leisure recreation, [but with] dark tourism, the sun went down. The lights went out," said Kirshenblatt-Gimblett. In that sense, "9/11 is no different from any number of sites in the world where something of cataclysmic importance happened and where there is a moral imperative to remember it, to commemorate it, to feel it," she said.

Joe Daniels, President of the National September 11 Memorial & Museum, acknowledges that labeling it tourism does "have some kind of negative connotation." But he also has a more idealistic view of tourists who are interested in experiencing a piece of 9/11 while visiting the city: "I would be very concerned if we didn't see this amount of interest—if we were overestimating how much people cared about 9/11 and what happened on that day."

Not everyone is as comfortable with the industry which has grown around 9/11: "There's no emotion behind [the visits.] It's like, Let's walk to the South Street Seaport and then let's walk to the trade towers.' There's something that's been removed," said Celia Marcelino. Her brother John summed up the difference: "When I first came to this building about one and a half years ago, everybody that walked in was really quiet. Now it seems little more like a Disney World attraction."