Peru Two Michaella McCollum has complained about the lack of privacy in prison which meant she had to regularly advert her eyes to inmates having sex.
The convicted drugs mule, who was locked up for trying to smuggle £1.5m-worth of cocaine in her luggage, said the women would openly get together behind bars.
She often "didn’t know where to look" but was "barely acknowledged".
The 26-year-old claims some of the female inmates were known as “chetos” and used for sex, but many of the other prisoners craving affection would also join in.
Writing in her new book, You'll Never See Daylight Again, she said: “When you’re sharing a bedroom with 99 other people any right of privacy is out the window.
“You see each other shower, you see everyone peeing, what’s a bit of sex between you and your most intimate 200 mates? I have to admit to being surprised by a couple of the relationships.
“The chetos signposted their sexuality. Any time they hooked up with one of the more feminine inmates I wasn’t surprised, except when they found each other.
“Others spent so much time showing me pictures of their children and husbands I had to do a double take when I saw them face down in someone else’s cleavage.
"When their bloke visited, they’d be all over him. But for those cold winter nights in between they had alternative sources of comfort.
“And when they got down to it they were so passionate it was like the world was ending. I was transfixed by their intensity. I’d never seen anything like it.”
Michaella, from Northern Ireland, was 20 when she and pal Melissa Reid, from Scotland, were arrested in the airport at the capital city of Lima in 2013.
She was initially sentenced to more than six years behind bars, but served just over two years in the maximum security prison.
She was released in March 2016 and has since given birth to twin boys.
Describing one sex act between two inmates, she said: "I was chatting when I got a nudge from the girl on the other side of me. I turned around.
“The girl on the other side of her was off the bench, her trousers and pants round her ankles, and my neighbour was [performing a sex act].
“Just like that, right next to me, in front of hundreds of prying eyes. It was a weird situation.
“Every single person around the table carried on sewing and chatting or watching as if it was the most normal thing in the world.”
As Michaella also claimed she was handcuffed, stripped naked and told she'd "never see daylight again".
