Tucked at the western base of the Palazzo Ducale is an extraordinary piece of Renaissance engineering: a wide spiral ramp climbing through the rock from the former stables (the Data) to the palace courtyard far above. Big enough for horses, lit by occasional windows, it allowed the duke's household to move animals and goods invisibly into the palace.
The Data itself is now an exhibition space; the ramp can be walked end to end and is included with the Palazzo Ducale ticket. The entrance is on Via Mazzini below the palace, easy to miss. The cool, echoing climb is unlike any other interior in the city.