I do like the work of Glasgow architect and designer Charles Rennie Mackintosh.
This is Scotland Street School designed 1904 and 1906. Mackintosh liked to include aspects of Scottish castles in his designs and in this school he has placed the stairwells in two circular towers, one at each end of the building.
Somewhat surprisingly there are blue and green coloured tiles inside contrasting to the red sandstone exterior. These colours have also been used in the patterns of leadlight glass.
I really like the simple pattern high in the curved windows of the towers consisting of two green triangles, standing on their points one on top of the other, combined with two glass panels split into a regular grid. This pattern is repeated across the windows in a horizontal band leaving the bulk of the area as clear glass. I find it very appealing.