In the diverse collection of documents preserved in the Veneranda Fabbrica's Archives, one of the most significant sections is that dedicated to historic drawings, where one can track down numerous valuable designs and studies regarding not only the Cathedral's architecture, but also its decorative aspects and even furnishings.
Among these are various drawings by Giuseppe Vandoni, an architect for the Veneranda Fabbrica from 1861/62 to 1877. Vandoni is known in particular for having given his name to one of the four small spires positioned on the sides of the lantern spire which supports the Madonnina and, specifically, the one located to the north-west. The architect oversaw the design of many fundamental parts of the Cathedral, for example the Altar of Saint Giovanni Bono, the storage area and the underground tunnel, the bronze doors, and the interior furnishings, as well other functional elements that are often overlooked by distracted tourists and visitors.
This interesting, yet often mistreated category of "minor works" contains some truly interesting pieces, including the drawing shown here (AVFD, Fondo Vandoni, Cart. 1: Facciata, tav. 34). Dated 1867 and accompanied by an inscription that reads: "Grating for horizontal windows open in the underground vault of the Duomo di Milano […] which serves as a storage area for chairs, pews, and various other objects." The gratings being referred to are still visible between the marble inlays of the Duomo's floor, despite the fact that the dizzying Gothic height of the Cathedral draws one's gaze up towards the capitals and the vaulted ceilings in a sweeping gesture of heavenly vertical tension.
During your next visit to the monument, the internationally recognized symbol of Milan, direct your eyes downwards and attempt to retrace the details of the "history" on which you are walking.