In Peter Jackson's movie the towers referred to are Barad-Dûr and Orthanc, although in the book The Two Towers the towers are Orthanc and Minas Morgul.
In Peter Jackson's movie the two towers referred to are Sauron's Barad-Dûr and Orthanc. While in the book The Two Towers the towers of the title are Orthanc and Minas Morgul.