Columbia subject headings:
Castles--Great Britain--Guidebooks.
Castles--Great Britain.
Castles--Ireland--Guidebooks.
Castles--Ireland.
Harvard subject headings:
Castles--Great Britain
Castles--Great Britain--Guidebooks.
Castles--Ireland
Castles--Ireland--Guidebooks.
Princeton subject headings:
Castles--Great Britain--Guidebooks.
Castles--Great Britain.
Castles--Ireland--Guidebooks.
Castles--Ireland.
Guidebooks.