From Fritz Leiber's story of the same name. The Gray Mouser finds the black wall.
About ArtStation Art Posters
ArtStation Art Posters are a giant leap above standard posters by offering superior print quality and finish. Enjoy rich, vibrant colors with a beautiful satin finish that make artworks pop. ArtStation Art Posters are giclee printed on heavy 240gsm premium satin paper with a waterproof, micro-porous, resin coated surface. Archival pigment inks provide light-fade resistance for generations.