Sismondo Castle and Fortress
Rocco Malatestiana is quite impressive... well, all castles are. It was both the residence of the Malatesta family (the lords of Rimini in 13th-17th c.) and a fortress, and was designed by Sigismondo Malatesta himself.
When there's the weekly market in Rimini, the vendors' stands extend from Piazza Cavour towards right by the castle in Piazza Malatesta. It made me think that the market was probably an echo of a local custom in the Middle Ages
Today the castle houses the Museum of Extra-European Arts (also called Primitive Arts), the exibits come from Africa, Oceania, and Pre-Columbian America.