Hubert H. Humphrey Metrodome, Minneapolis, 2007.

Hubert H. Humphrey Metrodome, 501 Chicago Avenue, Minneapolis, 1982.

Dilley Hall, Shattuck-St. Mary's, Faribault, 2016. Photograph by Paul Nelson.

Platteville Limestone, Church of the Assumption, St. Paul, 2016. Photograph by Paul Nelson.

Platteville Limestone curve of the Church of the Assumption, St. Paul, 2016. Photograph by Paul Nelson.

Abandoned bridge pier in the Mississippi River, downtown Minneapolis, 2016. Photograph by Paul Nelson.

Cathedral of Our Merciful Savior, Faribault, 2016. Photograph by Paul Nelson.

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.