Dutch police have seized 2.5 tonnes of methamphetamine with a street value estimated in the hundreds of millions of euro.
Police said it is the largest haul of the drug to date in Europe.
Spokesman Thomas Aling said there had not yet been any arrests following last week's haul.
"We are after them," he added, referring to the owners of the seized drugs, which he said had been destined for export, possibly to eastern Europe.
"You couldn't get rid of this in the Netherlands," he said.
Recent wastewater tests have shown that meth usage levels in Dutch cities is relatively low compared to the United States or Australia, but is rising.
Police uncovered the drugs while visiting an office building in Rotterdam as part of an ongoing investigation, they said in a statement.
They noticed that the second floor appeared smaller on the inside than on the outside.
They then discovered a concealed room where the drugs were hidden, divided into brick-size packages and stored in a large number of plastic shopping bags.
Subsequently police also uncovered a warehouse in the city of Utrecht with 17,500 litres of chemicals used in washing cocaine or producing synthetic drugs.
At the same location in Utrecht, police also found hollowed-out rocks they believe were used to transport the drugs.
The drugs have been destroyed, the police said.
