A bathroom should be a sanctuary of privacy. But what feels private to some people may feel uncomfortable to others. Privacy requirements can vary from one type of bathroom to another. A powder room, for example, will have different requirements than a master bath with views of a secluded backyard.
In any case, you'll probably want coverings for large windows. Avoid heavy fabrics that will soak up moisture. Quick-drying cotton is best, though you may need a liner to avoid transparency. Other options include venetian blinds, miniblinds, and pull-down shades. Don't use wooden blinds or shutters unless your bath has excellent ventilation to get rid of moisture.
Glass block allows in light while obscuring views. It can be used for internal partition walls (such as shower enclosures) or in window openings. Some kinds of glass block distort views and conserve heat more than others, so choose a pattern that makes you feel comfortable.
Narrow, horizontal windows placed high on a wall are another possible solution. Remember, however, that just because you can't see out doesn't mean someone else can't see in. A high window in, say, a first-floor bath may be within view of a neighbor's second floor.
In addition to visual privacy, acoustic privacy is a concern in bathrooms. The whir of a ventilating fan can act as welcome white noise, drowning out other sounds. Insulating the bathroom walls also helps. Look in home centers for insulation and wallboard fasteners that are specifically designed to deaden sound.