Frommer's Guide, referenced in the New York Times, has this interesting review about Singer Castle:
"this dramatic medieval castle is worth going out of your way to see. It's a stunning creation, made of the same granite used for Boldt Castle and erected at the same time in the first years of the 20th century. Unlike its sister castle, however, Singer was actually occupied, and it's still furnished with period pieces."
Of course, the above review is entirely correct. However, if I may critique the critique, the reviewer's source did get one thing slightly askew. The review related to: "... Bourne's secret passageways and peepholes used to spy on guests." That is actually a late-date myth, albeit close to the truth. The castle was actually built with hidden passages so that the servants could move unobtrusively about the castle without being a bother to the guests. They could then attend to the guests' needs without creating any disturbance. If one can define the word spy without the nefarious connotation, that will be the correct idea.
Click on this blog's title to see the entire review in the New York Times.