Columbia subject headings:
Castles--Germany--Eifel--Guidebooks.
Eifel (Germany)--Guidebooks.
Fortification--Germany--Eifel--Guidebooks.
Harvard subject headings:
Castles--Germany--Eifel--Guidebooks.
Eifel (Germany)--Guidebooks.
Fortification--Germany--Eifel--Guidebooks.
Princeton subject headings:
Castles--Germany (West)--Eifel--Guidebooks.
Eifel (Germany)--Guidebooks.
Fortification--Germany (West)--Eifel--Guidebooks.