The staff at Duolingo has a good sense of humor. For the "Household Badge" --(I can't help it that they all look like Boy Scout badges)-- there's a drawing of a toilet, in it !!
NOW, what was that word for "toilet", in Spanish? "Retrete", I think. (That gives "new meaning" to the English phrase, "I'm going on retreat this weekend". Hmmm! An outdoor "retrete", maybe?
YES, the above is just a play on words. But, isn't it the humor that keeps a language "new and interesting", every day?
ENJOY your studies of the Spanish language! Remember not to forget the humor, as you go along.
Now, where's the toilet paper for the "letrina", when you need it.....
In modern Spain it's not that common anymore to use the word "retrete", at the very least it's out of trend. It actually does mean "retreat", because you retreat to a private place to go poop, which I think is a very funny euphemism. Nowadays the most common way to call it in Spain is "baño", which is another euphemism (because you are not actually going to have a bath). Also "servicio(s)" is very common, especially when referring to public toilets.
"Letrina" is not euphemistic, but it's not that used either. This word actually makes me think of a disgusting collective toilet, like in some military barracks.
Note that these are exactly a kind of words (the euphemistic kind) that tend to change a lot from country to country, so it might be very different outside Spain.
I'm familiar with baño in Mexico as well. I'm sure that I must have used it on one of my trips to Mexico, and I think if they would have looked at me funny, I probably would have noticed.