Fort Thüngen is a historic fortification in Luxembourg City sited in Dräi Eechelen Park. Named after the Austrian commander-in-chief of the fortress, Baron of Thüngen, it was built in 1732 to enclose the defence work called Redoute du Parc (Park Redoubt) set up by Vauban 50 years before. A deep moat surrounded Fort Thüngen which was accessible only through a 169-metre long underground tunnel through the rocks from Obergrünewald. In 1836 the Prussians extended the Fort and in 1860 strengthened it again.
Most of the original fortress was demolished after the 1867 Treaty of London, which demanded the demolition of Luxembourg City's numerous fortifications. The three towers and the foundations of the rest of the fort were all that remained. During the 1990s, the site was reconstructed in its entirety, in parallel with the development of the site for the construction of the Mudam, Luxembourg's museum of modern art.
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.