Old-World bathrooms are often characterized by traditional "Old-World" or European design elements. They tend to be bright, airy and open spaces, filled with classic features like claw-foot tubs and porcelain pedestal sinks.
One of the keys to creating an Old-World bathroom design is to steer clear of synthetic materials as much as possible. Plastics and other synthetics didn't exist in the Old World, and they'll feel no more at home in your bathroom design than they would have there. Stone, wood, glass and porcelain, however, are great materials to use for an Old-World bathroom.
When it comes to fixtures and furniture, don't be afraid to go big, assuming you've got the space. Tubs were particularly grand affairs in the Old World, so a dramatic claw-footed tub makes a great focal point for the bathroom.
For accessories, consider wrought iron, wood or stone for things like bath towel racks or mirror frames. These materials were all prevalent in the grand bathrooms of pre-war Europe, and they'll feel right at home in your Old World bathroom design.
Finally, don't be afraid to experiment with pattern and texture. In particular, wallpaper in Old-World bathrooms is often intricately designed and artistic.