The castle was built in 1385 by Bartolino da Novara, commissioned by Niccolò II, to defend the d'Este family against uprisings, and was joined to the Palazzo Ducale by a covered and elevated passageway still in existence. From the 16th century onwards it became the new court residence, involving radical changes in the structure of the fortress, such as the replacement of the merlons with marble balustrades, the building of the roof-terraces on the towers, the addition of a storey and creation of spacious apartments. Inside you can visit the old kitchens, where the signs of the large fireplaces used for the preparation of the famous banquets by Messer Messisbugo can still be seen, the prisons, where the unfortunate lovers Ugo and Parisina were incarcerated before being killed, and, on the first floor the Loggia, the "Orange Garden", the Saletta dei Baccanali, the Chapel of Renée of France, wife of Ercole II, the Sala dell'Aurora, with frescoes representing the four parts of the day, and the Saletta and Sala dei Giochi, with scenes of games and sports. All the frescoes are the 16th-century works of Camillo, Cesare and Sebastiano Filippi and of their assistants.

The palace is named after the 12500 diamond bosses that decorate the façade of this building. The palace of Diamonds houses a modern art gallery, a museum devoted to the Risorgimento and the Pinacoteca Nazionale, which displays paintings showing the development of the Ferrarese, Emilian and Venetian schools of art from the 13th to the 18th century.

This palazzo, dating from the 14th century, is one of the grandest of Ferrara's palaces and used to be the summer retreat of the D’Este family. Famous for the rooms of the months, commissioned by Borso D’Este, whose walls are decorated with hunting scenes, groups of musicians, signs of the zodiac and classical legends by Tura’ and other Ferrarese painters. The palace houses also a museum, Museo civico di Arte Antica, which displays archaeological collections, medals and bronzes.

More Renaissance palaces lie in the south-eastern quarter of the city centre, lining the wider streets above the tangled medieval district, one of which, the Casa Romei is typical of the time, with frescoes and graceful courtyards alongside artefacts rescued from various local churches.

This delightful single-storey building, finished in 1559,was where Marfisa D’Este used to hold court, attended by her friends, among whom the Italian poet Torquato Tasso. The residence was once surrounded by loggias, gardens and pavilions, but only little remains of all that splendour. Nevertheless you can still admire the loggia degli aranci and the interior ceiling decorations of the 16th century.

The Palazzo Comunale, built in 1243 but much altered since, holds statues of Nicolò III D’Este and of Borso, one of his reputed 27 children, on its facade, though they're twentieth-century reproductions. The originals date back to the 15th century and are by Leon Battista Alberti.