Nearly three years after buying the Pontiac Silverdome for $583,000, a Canadian real-estate investor has snapped up another bargain in the Detroit region.

A company controlled by the Apostolopoulos family, of Toronto, has purchased the landmark Penobscot Building, Detroit's third-tallest office tower, for $5 million. The price, which comes to $5 a square foot, is tiny compared with the $200 level that buildings on average are selling for nationwide and even well below the $28 range that downtown Detroit buildings fetched last...