This happened many years ago in a New York hotel. It was in August, so very hot, and the aircon sounded like a 747 on takeoff, so I left it off and slept au natural, just under a sheet.
The first morning, I head a knock on the door first thing (say 7.30am) and the door opened, I don't know why but the chambermaid was checking every room, opening the door then saying sorry or something. I was just about covered by the sheet, but only just and I thought that was a close thing. This happened again the next morning, so I decided the following morning to throw the sheet back, but lie face down, so that she would see my bottom, but in very dark light.
One morning, she came in while I was drying myself in the bathroom, but out of her view.
For my final morning, I decided to give her a frontal view. I left a tiny crack in the curtains - the sort you'd easily miss at night, but would provide decent light in the morning. Naturally, as I was 'asleep' I wouldn't notice this, and wouldn't notice that this light was perfectly positioned to illuminate my cock
As I heard her going down the corridor, I positioned myself, shut my eyes and waited. The knock came, and the door opened. In reality it probably wasn't that long, but seemed like an eternity before she shut the door again, clearly she had had a good look at me naked, and my exposed cock.
A massive turn on at the time, being 'voyeured' like that, I wonder what she told her friends!