The hilltop at Dybbøl, two kilometres west of town, is one of the most important sites in modern Danish history. It is where the Danish army was decisively defeated by the Prussians in 1864, ending Denmark's claim to Schleswig and reshaping the country into the modest state it has been ever since. The white windmill on the ridge has been destroyed and rebuilt several times; it is the symbol of the battle.
The Dybbøl Banke History Centre (Historiecenter Dybbøl Banke) is an excellent modern museum at the centre of the battlefield, with reconstructed Danish trenches, a film, and well-lit displays. Outside, the redoubts and earthworks are still visible across the open hillside; you can walk between them in about an hour. The mill is open in summer.