The above sentence I encountered during Article usage practice.I answered that there should be a the before last summer but my teacher pointed that the should be placed before norther areas.The teacher didn't give me a satisfactory explanation.Shouldn't it be "We visited northern areas of our country the last summer." as use of the before directions or geographical regions is prohibited.
There is potentially a slight difference in meaning between " northern areas" and " the northern areas". The former can mean some of them, the latter tends to mean all of them. "We visited northern areas of England but did not go to the Lake District" would, I think sound odd if "the" had been inserted.