The Visible Windows mod improves the look and feel of the various windows that you see in tows and villages across Skyrim.
The vanilla textures for window glass, most frames, railings, and detailings have been replaced with brand new textures. Needless to say, these new textures look fantastic.
The photo here will give you some idea but if you're looking for more, take a look at the video below. Visible Windows shows up at the 5 minute, 33 second mark.