A few years back I was on a sports summer school in Holland. At the end of the morning training session I went to the normal changing rooms but they were packed so I found another set further down the corridor that were empty. The shower room was just an open room the same size as the changing room, with a dozen or so wall mounted jets and no cubicles or curtains. I was busy soaping up when the door opened and 2 women walked in chatting away in Dutch. The first thought that went through my mind was I'd gone into the women's changing room and showers but they didn't say anything so I carried on showering.
Later as I left the changing rooms, I did check the sign on the door and it was a men's changing room!