This happened a number of years ago. I was on holiday in Ireland with my wife and our young child. I'd always fancied trying windsurfing so, with my wife's agreement, I booked a day's lesson at a watersports centre.
My wife dropped me off there in the morning and arranged to pick me up at the end of the day.
I had with me a pair of swim trunks, a towel and a packed lunch. Everything else was provided by the watersports centre.
When I arrived and booked in I was provided with a wetsuit and directed to the male changing room. It seemed mine was the only 'day' booking, the remainder of those taking part in the day's lesson were resident at the centre. They were a mix of ages, families, couples and singles -- about a dozen of us in all.
Nothing eventful happened during the lesson (except that I fell over a lot!).
At the end of the lesson we returned to the centre and, after helping to store away the equipment, the others went off to their accommodation to shower and change and I was directed back to the male changing room, through a door directly from the outside of the building. As the only day visitor, I had the changing room to myself. On entering, I noticed that the internal door from the reception area into the changing room, by which I had entered in the morning, had been left open. However, as I had left my clothes hung on a side of the room out of the line of sight from the door, this did not concern me.
I peeled off the wetsuit that I had been loaned for the day and then removed my trunks. I looked around for the showers and realised that to reach the entrance to the shower room I would have to walk across the line of sight from the open door. I wrapped my towel around my waist and walked across to the shower room.