"El baño de mujeres está atrás."
Translation:The women's bathroom is in the back.
at the back, or out the back are equally correct. Only Americans say 'in back or in the back' unless you are 'in the back of a car, for example.
"Out back" definitely implies OUT of the current building. In a bar if you told someone the bathroom was "out back" they'd be looking in the alley. You would say "IN back" in English to mean "go toward the back of the building".
Americans (mid-Westerners, at least) also say simply "in back." This was marked incorrect.
Saying it is "out back" makes it sound like we're talking about an outhouse or something!
I normally say "women's room" or "ladies room" for a public bathroom. I would never say "bathroom" as well as specify the gender.
Well, suppose we’re at a hostel or some such thing with separate showers/bathrooms for men and women. This would be a very useful sentence indeed.
Not all dialects of English are American dialects. "At the back," is also valid.
'In the back'? The former colonials are getting their own back by executing a reverse colonisation of the mother tongue. O tempora o mores.