Columbia subject headings:
Astronomical observatories--Italy--Padua--History.
Castles--Italy--Padua--History.
Harvard subject headings:
Astronomical observatories--Italy--Padua--History.
Castles--Italy--Padua--History.
Princeton subject headings:
Castello di Padova (Padua, Italy)
Castles--Italy--Padua.
Padua (Italy)--Buildings, structures, etc.