The only Nazi concentration camp on Italian soil, built in 1898 as a rice-husking mill and converted by the SS in 1943 into a transit and extermination camp. Today it is a national monument and museum — sobering, important, and unmissable for anyone with an interest in the Second World War in Italy.
The site is about 3 km south of the city centre. Allow at least 90 minutes. Admission is free; the audio guide (€3.50) adds significant context. As with Miramare, factor in travel time and do not try to combine both in a single day.