Hang drapery over the den windows either to block out light or sheer fabric to let in soft sunlight. Pick drapery colors that match with accessories in the den and use matching ones on each window. Opt for a valance that covers only the top half for a splash of color around the window.
Decorate the windows in the den to celebrate the different holidays or seasons. Use window clings that depict seasonal accents like fall leaves, patriotic displays or winter elements. Rotate them throughout the year to create a festive atmosphere in the den.
Create paintings directly on the window using stained glass paint. Depict entire scenes that fill the entire den window or make a decorative border around the glass.
Apply a layer of decorative film on the den windows. Use film specifically designed for windows, which comes in a range of styles, from ones that are for privacy to ones with strictly decorative appeal.