Columbia subject headings:
Architecture, Domestic--Germany--Ruhr (Region)
Architecture--Germany--Ruhr (Region)--History--19th century.
Architecture--Germany--Ruhr (Region)--History--20th century.
Harvard subject headings:
Architecture, Domestic--Germany--Ruhr River Valley.
Architecture, Modern--19th century--Germany--Ruhr River Valley.
Architecture, Modern--20th century--Germany--Ruhr River Valley.
Working class--Dwellings--Germany--Ruhr River Valley.
Princeton subject headings: