When we looked at our house the first time, I assumed the closed door beside the bathroom was a closet so I didn't even open it. Surprise! They are both in the hallway adjacent to the dining room. Our house was built in the 1940's so I'm certain it's not an original feature.
Don't get me wrong, it's not the worst design flaw I've seen in a house. We've made the most of it and I've come to like the idea of the girls potty and the boys potty. I never cared for sharing with my husband anyway :)
I decided to start with the girls bathroom, you know since it's the one I look at more than just on cleaning day. Even when we moved in I didn't do much with it, so it was easy to make it what I wanted.