Platteville limestone arch, Mill Ruins Park, Minneapolis, 2016. Photograph by Paul Nelson.

Limestone seam under Stone Arch Bridge, 2016. Photograph by Paul Nelson.

Commercial building, Central Avenue, Minneapolis, 2016. Photograph by Paul Nelson.

Fort Snelling Chapel, 2016. Photograph by Paul Nelson.

Fort Snelling Hexagonal Tower, 2016. Photograph by Paul Nelson.

Fort Snelling Round Tower, 2016. Photograph by Paul Nelson.

Washburn A Mill ruins, 2016. Photograph by Paul Nelson.

The Alexander Ramsey House, 2012. Photograph by Wikimedia Commons user McGhiever.

Willis Hall, Carleton College, ca. 1890s.

Old Customs House, Minneapolis, 1876.