Two people allegedly romped on the grass up Plymouth Hoe to the astonishment of shocked passers-by.
Witnesses enjoying the evening sun said they were looking across the beauty spot when they spotted a male's "questionable arm movements" at around 8pm on Wednesday, May 20.
On closer look, witnesses saw a woman "bounce up, lift her dress" and "hop" on top of a man.
Witnesses say a woman's bottom was on display, and a man appeared to be nude.
A video from the scene appears to show a third person, partially nude, nearby.
One witness said: "There was ''no subtlety whatsoever.'
"Chocolate button out, the lot!" they said.
"They were at it shamelessly for a good 15 minutes. The guy kept looking over her shoulder in our direction and that of anyone walking past."
The witness said they considered approaching the couple and asking them to stop as there were young people nearby, but didn't want to cause a scene.
Plymouth Live understands another witness reported the matter to Devon and Cornwall Police.
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One witness, who just ten minutes previously noticed an allegedly drunk person urinate on themselves, labelled the incident "live porno".
She said she and her friend "just couldn't believe what was happening".
"[It] felt like the world has gone mad," she added.
Another witness, who filmed the activity, told Plymouth Live: "People having sex in front of children at 7.30pm. Talk about lockdown!"
What does the law say?
While there is no law banning sexual intercourse in public places per se, people can be prosecuted if they expose themselves to others and/or "outrage public decency".
"Outraging public decency" is a common law offence and was formerly regarded as a form of public nuisance.
The offence can consist of any act or display that is "lewd, obscene or disgusting to such an extent as to outrage minimum standards of public decency as judged by the jury in contemporary society."
To constitute as outraging public decency, the behaviour "must occur in a place which is accessible to or within view of the public" and "two or more people must be present" during the act or display, whether or not they are aware of the act or display or are outraged by it.
According to the Law Commission from the UK government, the types of conduct that are considered to outrage public decency are wide ranging.
They include: indecent exposure, masturbating or other sexual activities (real or simulated) in public, intimate filming of women without their consent, nude bathing in inhabited areas, procuring girls to be prostitutes and urinating on a war memorial.
