Koldinghus is a Danish royal castle in the town of Kolding, 50km east of Billund. Its origins date to the 1200s, when it was built as a border fortification on the old frontier between Denmark and the Duchy of Schleswig. The castle was expanded by successive Danish kings through the 16th century, becoming one of the most important royal residences in Jutland. A fire in 1808 gutted most of the structure, and the ruins stood open to the sky for nearly two centuries before a careful restoration project in the 1990s stabilised and reroofed the building.
Today Koldinghus houses a museum of applied arts and decorative objects, with a permanent collection of Danish silver, furniture, and design from the medieval period to the present. The restored great hall and chapel give a sense of the castle's former grandeur, while the half-ruined towers and courtyards are impressive in their own right. The surrounding gardens overlook Kolding Fjord. Worth a half-day if you have a car, particularly in combination with Vejle (20km north). Kolding itself has an attractive centre with some good cafes.