Columbia subject headings:
Harvard subject headings:
Architecture, Medieval--Germany--Congresses.
Architecture, Medieval--Germany--Schleswig-Holstein--Congresses.
Castles--Denmark--History--Congresses.
Castles--Germany--Lower Saxony--History--Congresses.
Castles--Germany--Mecklenburg-Vorpommern--History--Congresses.
Castles--Germany--Schleswig-Holstein--History--Congresses.
Schleswig-Holstein (Germany)--History--Congresses.
Princeton subject headings:
Castles--Germany--Schleswig-Holstein--Congresses.