The Giant Wheel, plate 9 from Imaginary Prisons

From the Carceri d’invenzione, the imaginary prisons. Piranesi first issued them around 1749–50 and reworked the plates about a decade later, darkening them considerably.

They are architecture that cannot be built: staircases that arrive nowhere, machinery at a scale with no purpose, space that continues past every edge of the sheet.