Built under Habsburg rule as a defence against Turkish attacks, Osijek's compact 18th-century citadel was relatively undamaged during the war in the 1990s. This baroque complex of cobblestone streets, spacious squares and stately mansions reveals a remarkable architectural unity, lending it the feel of an open-air museum, yet one still very much in use today. Many of the mansions are now used by various university faculties and as secondary schools so there's a lively, youthful buzz to the cafe-bars here.