Like a lot of people, I have numerous windows in my home that are over doors or other windows or just in an odd place that can't be treated with drapes. Why not fill them with an iron piece to help make them more decorative. Just take your measurements and account for any odd shapes. They can be set in the opening or hung. It depends on how much of a ledge you have or if you have a lot of movement in the wall (doors closing, etc.)
This is an odd modern-shaped octagon window I have in my non-modern house. I used a bold graphic circle piece to try to draw the eye away from the shape of the window. It was a frame to a broken mirror in an as-is section. It is hung with a single hook using the mirror's original hanging hole.
This is over my front door and is an eyebrow window. I needed a cascading piece to account for the arch. This is just leaned in the window (it is lighter and has never even moved no matter how much the door has been opened and closed).
This is over my study doors and was originally filled with a "lovely" etched glass piece. After I replaced the glass myself (that will be another post), I hung this piece to give the blank area some interest. Double duty because it can be seen from both the study and the master bedroom.