Columbia subject headings:
Castles--Germany--Main River Valley--Guidebooks.
Fortification--Germany--Main River Valley--Guidebooks.
Main River Valley (Germany)--Guidebooks.
Harvard subject headings:
Princeton subject headings:
Castles--Germany (West)--Main River Valley--Guidebooks.
Fortification--Germany (West)--Main River Valley--Guidebooks.
Main River Valley (Germany)--Guidebooks.