Mine (or at least one of them) goes back decades. 20 years at least!
I was once travelling on the 'up' escalator in Top Shop in the Gallowgate end of Eldon Square. For some reason I cast a backward glance and the extra height on the escalator allowed me to peek a view of a couple 'getting it on' in a ladies changing cubicle. With the escalator still going upwards it was a momentary vision, so fleeting that I had to go down the stairs and back up again to confirm what I had witnessed.
I hope you don't regard my interest as strange but I found the whole scenario very erotic.
It hasn't become an obsession but from time to time it crosses my mind, but everywhere seems so well policed these days, attendants, etc., that it remains an unfulfilled fantasy!
Any thoughts who might be up for it as an outcall?