One of the first vital phrases you learn in English class is usually :
“May I go to the washroom?”
If someone is traveling they will always find “Excuse me, where is the bathroom?” in their phrasebooks.
But we have so many names for that room: Washroom, Restroom, Bathroom, Lavatory, Toilet, W.C. … which one is best to use?
In Canada we usually say “Washroom” or “Bathroom”. In other parts of North America they also use “Restroom” fairly often. To North Americans it would be strange to say “I need to use the toilet.” Some parts of America find the name “Bathroom” strange to use, since it doesn’t often have a bath in it.
When I went to Australia people commonly called that room the “Toilet”, I’ve heard that’s common in England too.
I’ve heard in Britain they call that room the W.C. (water closet) or lavatory. But those words would be strange to use in North America.
Then there are a whole bunch of slang: “The men’s room / the ladies room”, “The loo” (Britain), “the facilities” and also some less polite slang like “The crapper” or “The pisser”.
So even native English speakers get confused with these. It seems that “Washroom” is the safest one to use overall. But if you are visiting an area find out what the locals call it.