Benevento's compact historic centre packs in a remarkable density of ancient monuments. Start with the Arch of Trajan, the best-preserved triumphal arch in the Roman world, then follow the old town uphill to the Duomo and its extraordinary 12th-century bronze door. The Church of Santa Sofia and its attached cloister — together housing the Museo del Sannio — are around the corner. The Roman Theatre on the east side of the old town preserves most of its cavea. Near the Arch of Trajan, an Egyptian Obelisk from Domitian's Isis sanctuary stands in Piazza Papiniano.
Most of this can be covered on foot in half a day. The city is genuinely off the tourist trail, and you are unlikely to encounter another foreign visitor at any of these sites.