Can you post some pics and give more details? :)

Sorry, house is in France & no pics. But it has plumbing through stone wall, an old porcelain shower pan, exposed beam on ceiling and floor is concrete. We are considering a glass partition and leaving existing stuff in place.

I think the main issue will be the condition of the plumbing. If you haven't thoroughly had it inspected, do that before starting any updating. The exposed beam sounds like a beautiful asset to the bath and the house as a whole. If you find the concrete floor unattactive, perhaps it could be stained or tiled over. Depending on the glass available, I would try to keep it in the style of the fixtures and the rest of the house. However, if you truly want to make over the bathroom to a modern style or to bring it up to modern standards, do it! Maybe there's way to modernize the plumbing and fixtures and keep it in the style appropriate to the rest of the house. A 400 year old house is way outside of this Texas girl's experience! I would LOVE to see pics! If at some point you are able to post some, please do!

Great points! We are thinking of staining the floor. Keeping the character of the house intact is top priority and we think less is more in this small shower room. Typical of France, the toilet is in separate adjacent room (but it is in the house!) May have pics after our next trip.

I hope it turns out great for you! :)