Since I've always worked in Chicago's financial district, my business trips to New York have been to the area of the World Trade Center, I was in the mall a few times (I still have a tie I bought there when I forgot to pack one). Most of my experience is with the North Tower though, and that's limited, just a visit to Window on the World. I don't recall anything memorable about the Twin Towers--they were just tall office buildings like the ones I'm used to in Chicago. And the mall was pretty much geared to meeting the day-to-day needs of the people who worked in the vicinity, not especially noteworthy either. I had a young relative who worked for a big financial firm in the area, and she eventually walked home through the dust to Brooklyn. Her immediate family was pretty concerned until they heard from her. The trading desks in the Twin Towers had open phone lines to some of the Chicago Exchange floors, so before communications stopped people in Chicago could talk to their co-workers in peril in New York. I saw the first news reports on a tv monitor in the train station. We spent the first part of the morning waiting to hear what was going to happen in the Chicago loop. Since our office was a block from Sears Tower, we were sent home before the morning was over out of concern of an attack against Chicago.
Mark may already know why people in the story are in New York, since he's asking about the towers, rather than how to get them there. But there's a Hollywood connection to one of the firms in the Noth Tower. Cantor Fitgerald earlier in 2001 had bought the Hollywood Stock Exchange, which was not a real exchange, but more of a game that lets people bet fake money on the success or failure of movies, stars, etc. HSX was a startup from the 90's that could have been invested in by Stefan and Brad, and that would have given them a link to Cantor, which lost more employees than any other tenant. HSX still exists. They tried to launch movie futures, which were approved a couple of years ago, but then outlawed by congress.