I once went to a house that had been stopped in the middle of construction for a couple of years, on a hill in the city. From this place, and only this place, the big living room window of a neighbor was visible. I watched as a guy got home, messed around a little, then reappeared naked with his cock in his hand, jacking happily to the whole city in the distance, and (unknown to him) to me a few yards away. The place had been abandoned for so long, I guess the guy there figured nobody would see him.
I was too startled to drop my pants, but I did watch him intently, and jacked off when I got home, and many times since, thinking of what I saw--it was very erotic!