Yesnaby Castle is a proper sea stack. Many people seem to think that Yesnaby Castle is a smaller version of the Old Man of Hoy and that comparison appears to have stuck. Yesnaby Castle, though, is a proper sea stack: it’s in the sea the whole time; and it’s a stack. The Old Man of Hoy may be taller but it is connected to the land of Hoy above the waterline and doesn’t qualify as a proper sea stack at all. Don’t worry, I’m a member of the Facebook Group Extreme Pedantry already.