Vandals smashed windows, threw paint on walls and turned on taps after breaking into a school building.
Yobs struck at the former Southfield Technology College in Moorclose Road, Workington, causing what police said was extensive damage.
The vandalism happened between 7.15pm and 10.45pm last night.
The broken windows have been boarded up.
A spokesman for the county council, which owns the building, said: "We have G4S Security Services patrolling the site regularly and police do regular drives past."
The site is no longer in use following the closure of the school at the end of term.
Its pupils, along with those from Stainburn School, will begin lessons at the new Workington Academy, on the Stainburn site, next week.
The future of the Southfield site is not yet known.
Anyone with information about the vandalism can call police on 101.
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules here