Since a 2014 inferno tragically gutted his landmark Glasgow School of Art, Hill House in the suburb of Helensburgh now represents the best remaining single work of architecture by Charles Rennie Mackintosh, one of the world’s finest practitioners of Art Nouveau. The ground floor appears much as it did when his client, publisher Walter Blackie, lived there in 1904. Mackintosh fretted over every detail, down to the decorative insets around the hearth. The house is a marvelous and unique structure, even by Glasgow’s high standards.