Back in our old house, when I was like 10-13, we had the furnace room right next to the bathroom. On the bathroom wall, inside the furnace room, it was unfinished. There was this small fan in the bathroom wall through which you could peer to see pretty much everything inside the bathroom.
Well, after finding this out, I used to spend a lot of time inside that furnace room, watching various people shower and so on, namely my sister's friends during sleepovers and sometimes, family.
My sister at the time was around age 11, a year or so younger than myself. I got home from school one day and was alone in the house. So, as I wanted to see more of her, I took a screwdriver and poked a tiny hole in the bathroom wall, between two tiles. You couldn't see it, unless you were specifically looking. After this, I waited for my sister to come home and watched tv.
When she eventually did, I knew she would hop in the shower, and into the furnace room I went, dick in hand. I watched her undress via the fan hole, while instantly getting a hard on. When she stepped inside the shower and pulled over the curtain, I moved to the hole in the wall. I could only see from her pussy to above her tits. I don't think I had ever had quite such an errection; I still remember it to this day. I watched as she soaped up her boobs (she was very large for an 11-year-old!) and stick her fingers inside her pussy to clean it.
It didn't take long before I came, and came I did. It was all over the floor, wall and my pants. I got out of there before she was finished, so she never had a clue.
From this vantage point, I watched many other females shower over time, and was never caught. Sucks we moved out of that place.