The Rocca, surrounded by lawns, is located in the heart of the small and characteristic historical centre of San Martino in Rio in Emilia: with a quadrangular plan, it preserves intact a square corner tower with Ghibelline battlements. It belonged to the Canossa family, the Roberti family, then to the Este family, and finally to Marquis Paolo Rango d'Aragona. Today it houses the Museum of Agriculture and the Rural World, the Coppelli Art Gallery, the Civic Library, the Historical Archive and the Open Archive for Henghel Gualdi.
Inside, the most significant rooms are: the 15th-century
Chapel of St. John, built in 1395, which still preserves the terracotta bands of the portal, the apse and the original Verona marble altar with the sandstone coat of arms of the Roberti da Tripoli family and a valuable St. Martin, also in sandstone; and some rooms with painted coffers, frescoes and stuccoes dating back to the 15th-18th centuries.
In the heart of the Torrazzo is the unicorn room: on the 14th-century structure, Borso d'Este commissioned its tempera decorations in the mid-15th century: some painters from the Erri family worked in
this period. The depiction recounts some 'exploits' of the House of Este, including the mythical animal.