Differdange Castle was built in 1577 although an earlier fortified castle of Differdange dates from around 1310. The first lord of the castle was Wilhelm, brother of the Lord of Soleuvre, who is mentioned in documents from 1310 when he owned a fortified castle. However, the lords of Differdange lasted only until the death of Wilhelm's grandson around the year 1400. When Soleuvre Castle burnt down in 1552, the owner Anna von Insenburg decided not to repair it but to build a Renaissance-style residential castle in Differdange serving both Soleuvre and Differdange. At the beginning of the 20th century, the castle came into the hands of the local steel industry, now Arcelor Mittal who used it as a hotel and a restaurant for its staff.
Differdange Castle is probably the earliest example in Luxembourg of a château built entirely in the Renaissance style. It was originally intended both as a residence and a fortification with a moat and draw-bridge (now both removed) as well as loop-holes. It is constructed fully in accordance with the principles of Renaissance architecture, especially the use of the square both for the courtyard and the outer walls of the three buildings which surround it. The rectangular cross-framed windows are typlical of the period. The octagonal towers which are slightly higher than the central building provide balance between the horizontal and vertical dimensions.
Since 1997, the castle has been let to Miami University for use as its Miami University Dolibois European Center.
References:First record of Kastelholma (or Kastelholm) castle is from the year 1388 in the contract of Queen Margaret I of Denmark, where a large portion of the inheritance of Bo Jonsson Grip was given to the queen. The heyday of the castle was in the 15th and 16th centuries when it was administrated by Danish and Swedish kings and stewards of the realms. Kastelhoma was expanded and enhanced several times.
In the end of 16th century castle was owned by the previous queen Catherine Jagellon (Stenbock), an enemy of the King of Sweden Eric XIV. King Eric conquered Kastelholma in 1599 and all defending officers were taken to Turku and executed. The castle was damaged under the siege and it took 30 years to renovate it.
In 1634 Åland was joined with the County of Åbo and Björneborg and Kastelholma lost its administrative status.