This church interior in Davids Samling in Copenhagen has a curtain in the foreground that at first appears as if it might be part of the main view, but then you see that it has a shadow on the surface of the canvas rather than on the pictorial content (and depth), a little like the (absent) readymades in Duchamp’s Tu M’ (see here) – the curtain is clearly meant to be a trompe-l’oeil covering for the painting. I quite like the way it can  be read either way.