Kalmar Castle is one of the best-preserved Renaissance castles in Scandinavia and the centrepiece of a visit to Kalmar. The building began as a medieval defensive tower in the 12th century, was transformed into a royal palace in the 16th century, and was renovated with enough care that the king's and queen's chambers look as they might have during the castle's heyday.
The rooms are decorated with original Renaissance details: painted wooden ceilings, tiled stoves, tapestries, and period furnishings that have been restored rather than replaced. The castle sits on a small island connected to the mainland by a short bridge, with a moat and outer walls that give it the look of a proper medieval fortress. In summer the courtyard hosts performances and events.
The castle's most historically significant moment was the signing (or near-signing) of the Kalmar Union in 1397, when the three Scandinavian kingdoms were united under the Danish queen Margarethe I. A good exhibition inside explains the political context. The castle also has a café and a pleasant walk along the harbour walls.