Grynau castle tower is situated at the then only bridge over the Linth river. Built probably in the early 13th century by the House of Rapperswil, the castle secured the strategically important river crossing in the area between the Grafschaft Rapperswil and the House of Toggenburg. The property was documented in 1311, when the castle was taken by force by Rudolf von Laufenburg-Rapperswil probably from the Toggenburg family.
In the summer of 1799, the French and Austrian troops fought in the Second Coalition War at the strategically important bridge which was destroyed three times, and rebuilt, and occupied by the French troops in the aftermath of the Second Battle of Zurich. Again in 1833, Swiss federal troops were concentrated at the Grynau castle, on occasion of the then planned division of the canton of Schwyz, however, waived without an armed intervention. And again in a Swiss civil war, the so-called Sonderbundskrieg, federal troops crossed the important bridge in March 1847, without a single dead soldier on both sides.
In the 19th century the remaining buildings, the tower, the adjacent barn and the former accommodation building, were bought by Schlossvogt Kälin, who rebuilt the surrounding building into the Landgasthof Schloss Grynau, a country inn, which is still held by the family.
The architecture dates back to the early 13th century. The five-story tower measures 12.5 x 12.5 metres, the foundation walls are 2.2 metres meters thick. The castle was between 1807 and 1816 widely rebuilt on occasion of the construction of the Linth channel; the road and bridge cross as of today in between the preserved tower and the former economic structures that were widely broken. In 1906 a fire broke out in the barn, which was adjacent to the tower and destroyed the roof and the interior of the tower. The castle tower was re-decorated and re-roofed and a new barn built in the following year.
The Gravensteen is a castle in Ghent originating from the Middle Ages. The name means 'castle of the counts' in Dutch. Arnulf I (918–965), Count of Flanders, was the first to fortify this place, building a medieval bastion on this high sand dune, naturally protected by the river Leie and its marshy banks. This bastion consisted of a central wooden building and several surrounding buildings, also in wood.
In the early 11th century, the wooden building was replaced by a stone residence, consisting of three large halls that made up three storeys, connected by a stone stairwell. The monumental stone staircase, the light openings, the fireplaces built into the walls and the latrines were signs of considerable luxury and comfort in those days. There was probably also a tower.