A young man and woman – who appear to be in their early 20s – were seen in the 15-minute romp on Saturday in Ware, Hertfordshire.
The couple “didn’t seem to care if anyone saw” despite the area being busy with people as a music festival rumbled on nearby.
Witness Kay Hamersley was having a cigarette by a window in her friend’s flat when she saw the young couple going at it hammer and tongs.
“The young man then pulled the girl to the stairs, bent her over and pulled her trousers down”
The 20-year-old then snapped what happened on her phone’s camera.
“First they were just standing looking at each other,” she told the Hertfordshire Mercury.
“The young man then pushed the girl to the wall and started to pull her trousers and underwear down. He then put his hand down her trousers.
“After a few minutes they stopped and went to walk away.
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“But as they were walking away, they then decided to do the same thing again but on a different wall.
“The young man then pulled the girl to the stairs, bent her over and pulled her trousers down. They started to have sexual intercourse.
“I couldn’t hear anything from where I was but they didn’t seem care if anyone saw what they were doing.”
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It came as the “Ware is the Music” festival rumbled on in the town.
“I was so shocked that I saw this happen, I couldn’t believe it,” Kay added.