Iberg Castle is located south-west of the town of Wattwil. The central keep is six stories tall and has an entrance on the north-west corner. The keep is surrounded by a curtain wall. The castle hill is protected by moats and some walls.
Iberg Castle was built in 1240 by Heinrich von Iberg who was a vassal of the Prince-Abbot of St. Gallen. The castle was briefly conquered in 1249 following the Toggenburg fratricide and again in 1290 during the rule of the anti-Abbot Konrad von Gundelfingen in St. Gallen. It was damaged during the Appenzell Wars in 1405 and soon thereafter rebuilt. During the conflicts leading to the Battles of Villmergen (from 1699-1712), the castle was besieged in 1710. After the Treaty of Baden in 1718 it was given back to the Abbot.
During the suppression of the monasteries in 1805, the castle became privately owned. Some of the housing was demolished in 1835, but the roof and battlements were rebuilt in 1902 and 1965 by the municipality.
References:Celje Castle was once the largest fortification on Slovenian territory. The first fortified building on the site (a Romanesque palace) was built in the first half of the 13th century by the Counts of Heunburg from Carinthia on the stony outcrop on the western side of the ridge where the castle stands. It had five sides, or four plus the southern side, which was a natural defence. The first written records of the castle date back to between 1125 and 1137; it was probably built by Count Gunter. In the western section of the castle, there was a building with several floors. Remains of the walls of this palatium have survived. In the eastern section, there was an enclosed courtyard with large water reservoirs. The eastern wall, which protects the castle from its most exposed side, was around three metres thicker than the rest of the curtain wall. The wall was topped with a parapet and protected walkway.