NEW YORK - More than three weeks went by since the Celtics last visited New York City, but Walter McCarty can't get a side trip from then out of his mind. Nor does he really want to.

McCarty was the only Celtic player among a group that toured the Ground Zero site of the Sept. 11 terrorist attacks and visited the Stock Exchange (Eric Williams went when the Celtics played New Jersey two weeks prior). The excursion brought the terrorist action - and the resulting U.S. response - to brighter light.

``Seeing it on TV, it looks unreal, like it couldn't happen,'' McCarty said before a 90-81 win over the Knicks last night. ``But once you go there it's very real and it's very huge. You wouldn't have any idea how big that space is down there until you go down there and see it firsthand.''

Having followed the events through the media, the trip