Very unique piece that I believe is 1910s-1920s era (not sure, acquired as-is). I believe this is a magic lantern slide

A magic lantern slide viewer is a device used to view glass slides with images, typically from the 19th or early 20th century. It works by shining light through the transparent slide and projecting the image onto a wall or screen, or sometimes allowing direct viewing through a magnifying lens. These viewers were part of early image projection technology and are considered precursors to modern slide projectors.