Columbia subject headings:
Castello sforzesco.
Milan (Italy)--Buildings, structures, etc.
Underground architecture--Italy--Milan.
Harvard subject headings:
Castello sforzesco.
Historic buildings--Italy--Milan.
Milan (Italy)--Buildings, structures, etc.
Underground architecture--Italy--Milan.
Underground construction.
Princeton subject headings:
Castello sforzesco.
Historic buildings--Italy--Milan.
Milan (Italy)--Buildings, structures, etc.
Underground architecture--Italy--Milan.
Underground construction--Italy--Milan.