Landowners are being warned to be vigilant after steps were taken to prevent an illegal rave from taking place in Wiltshire.
Police said they received intelligence about a gathering at a mine complex in Monkton Farleigh near Bath.
The owners of the mine have closed a car park but officers are worried that revellers might try to gain access through a disused works.
A spokesman said "illegal raves are potentially very dangerous".
He added that they "compromise public safety" and are disruptive to the local community.
A spokeswoman for Avon Wildlife Trust, which owns the site, said it was "very concerned" about the potential for trouble at Brown's Folly.
She said there had been a "history of party-going" at the site but the trust had recently improved some of the gates.
"The quarry is gated but people have broken in. If they are determined to get in they will get in," she said.
Wiltshire Police said patrols at the site would be increased over the weekend.
In August, an illegal rave in Marlborough attracted between 500 and 1,000 people.