Gothic Cathedrals 

1. Duke "Classic" Library Catalog - always use the old ("Classic") version for better and more accurate searching

  Use your natural language to find ONE book that's relevant.  Then go into the record and click the subject headings assigned to that book to find more like it.

These are all library subject headings

Architecture, Gothic -- Europe -- History -- To 1500.
Augustinian [or any order] architecture -- France -- [city]
Cathédrale de Chartres [or the name of an cathedral] -- History. 
Church architecture -- Europe -- History -- To 1500.
Civilization, Medieval, in art.  
Monasteries -- France -- [city]  

2. Worldcat - combined catalog of all libraries

  Use Worldcat to locate exhibition catalogs and books for interlibrary loan and archives of collections.  There's a "libraries with this item" link that shows NC libraries first.