Agents from the Civil Guard and local police forces from Spain's Murcia region carried out the raid which resulted in five arrests.
The raid uncovered 14,000 plants being grown in four huge greenhouses.
These facilities were "perfectly camouflaged" to fit in with other greenhouses and orchards in the agricultural zone of Puerto Lumbreras in Murcia, Spain's Civil Guard said in a statement.
The five men arrested were "experts" in the cultivation and genetic modification of cannabis, the statement also said. Production capacity was described as "enormous".
Police discovered the plantation after a robbery of the property carried out by four known criminals in the middle of August.
Those four men have also been arrested.