It is the mood of the beholder which gives the city of Zemrude its form. If you go by whistling, your nose a-tilt behind the whistle, you will know it from below: window sills, flapping curtains, fountains. If you walk along hanging your head, your nails dug into the palms of your hands, your gaze will be held on the ground, in the gutters, the manhole covers, the fish scales, wastepaper. You cannot say that one aspect of the city is truer than the other, but you hear of the upper Zemrude chiefly from those who remember it, as they sink into the lower Zemrude, following everyday the same stretches of street and finding again each morning the ill-humor of the day before, encrusted at the foot of the walls. For everyone, sooner or later, the day comes when we bring our gaze down along the drainpipes and we can no longer detach it from the cobblestones. The reverse is not impossible, but it is more rare: and so we continue walking, through Zemrude's streets with eyes now digging into the cellars, the foundations, the wells.
From: "The Invisible Cities" by Italo Calvino
"It is the mood of the beholder which gives the city of Zemrude its form."