Columbia subject headings:
Harvard subject headings:
Bolu İli (Turkey)--Antiquities.
Caves--Turkey--Bolu İli.
Church buildings--Turkey--Bolu İli.
Excavations (Archaeology)--Turkey--Bolu İli.
Princeton subject headings:
Bolu İli (Turkey)--Antiquities.
Caves--Turkey--Bolu İli.
Church buildings--Turkey--Bolu İli.
Excavations (Archaeology)--Turkey--Bolu İli.