Interested in a behind-the-scenes tour of Radio City Music Hall with architect Hugh Hardy? Or seeing site-specific dance in historic sites around the five boroughs of New York City? Or a peek at the Mark Morris Dance Center in Brooklyn? These and other arts-related events are part of the Open House New York weekend coming up on October 4 and 5: it's a great way for visitors, as well as local couch potatoes, to see some very interesting places. Info at www.ohny.org