The d 'Estes ' Palazzo dei Diamanti ( 9,000 pointed pieces of diamond-shaped marble on its walls ) houses the Pinacoteca Nazionale , with notable works of the Ferrara masters Cosmy Tura , Ercole de ' Roberti , Garofalo , and Dosso Dossi .
Pinacoteca Nazionale has been empty for the last 20 years .