Please answer the following question: Ontonagon Harbor Piers Historic District -  The Ontonagon Harbor Piers Historic District is historic shipping structure located on the Ontonagon River at Lake Superior in Ontonagon Michigan. It was listed on the National Register of Historic Places in 2001. Given a choice of categories company, educational institution, artist, athlete, office holder, mean of transportation, building, natural place, village, animal, plant, album, film or written work, the text refers to which one?
A:
Building