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Away to the west are the ruins of Noltland Castle , built by Gilbert Balfour in the 16th century , notable for its massive spiral staircase " second only to Fyvie Castle , while its triple tiers of gunloop s are without parallel in Scotland , if not Europe " .
 Gilbert Balfour
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
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Answer:
 Gilbert Balfour