The British Library has become a 'hotspot' for people being intimate in the toilets.
The central London institute has reportedly been forced to call the police over the use of the venue.
A complaint has been made to the library, near St Pancras station in central London, describing reports as being "totally unacceptable."
It comes after post on a "cruisers" advertises the library as being a meeting spot for casual sex with a "vast amount of toilets" on site, reports The Sun.
The British Library has said inappropriate behaviour 'is not tolerated'
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However, the site also warns of regular patrols of the facilities.
A spokesperson told GB News: "The British Library is a public institution and our site at St Pancras is visited by more than one million people every year.
"All of the Library’s public areas and facilities, including the toilets, are regularly patrolled by on-site security staff to ensure that they are being used appropriately.
"Inappropriate behaviour is not tolerated and the Library works closely with the police to ensure the safety and security of the Library’s buildings and users."
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The British Library has been forced to call the police
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One of the largest libraries in the world, it was historically part of the British Museum but became its own entity in 1973.
By law, the library is required to receive a copy of all books produced in the United Kingdom and Ireland.
Among its millions of artefacts, there is the only known surviving ancient copy of the poem Beowulf, two 1215 copies of the Magna Carta and The Diamond Sutra, the world's earliest dated printed book, printed in 868.
At the centre of the building, kept in a four storey glass tower is the "King's Library’", which contains around 65,000 printed volumes and documents collected by King George III between 1763 and 1820.
Earlier this year, the Library was hit by a major cyber-attack that shut down most of its services.
Personal data of staff and "readers", as its regular users are known, was stolen by the hackers and offered for sale on the dark web.
The library said it is still "[finding] ways to restore access to as much of our collection as possible, while ensuring that we do so in a way that is safe and resilient."