Iberg Castle, St. Gallen, Medieval castle ruin in Wattwil, Switzerland.

Iberg Castle is a ruined hilltop castle on a hill southwest of Wattwil at 740 m above sea level, overlooking the Thur valley between Lichtensteig and Ebnat-Kappel. Its irregular polygonal core is enclosed by a ring wall and holds a bergfried of 9 × 8.7 × 25 m with five storeys and walls 1.8 to 2.2 m thick. The old high entrance lies on the southeast side about 5 m above the courtyard; the tower is now entered at ground level via a reconstructed stairway. A ring ditch and ramparts protected the hill on three sides, while the south side drops steeply to the Hagbachtobel.

Iberg Castle was built after 1240, probably by Heinrich von Iberg, a ministerialis of the Prince-Abbey of St. Gallen, and first documented in 1240 as 'de Iberch'. It was conquered in 1249 by Count Kraft I of Toggenburg, besieged in 1290 by anti-abbot Konrad von Gundelfingen, and destroyed by the Appenzellers in 1405. After 1408 it was restored as a bailiff's seat; in 1710 it was occupied by rebellious Toggenburgers and slighted after 1718. In 1835 the roofs were demolished, and in 1901–1902 the keep was re-roofed and parts rebuilt.

The name Iberg probably comes from a field name, "Eibenberg", and was adopted by the ministeriales who first called themselves "de Iberch" in a document of 1240. From 1718 the abbey left the buildings to tenants who ran an inn inside them, and the complex then decayed.

You can find the castle ruins on Am Iberg street in Wattwil, easily located using coordinates 47.2975°N and 9.08°E. The site is accessible on foot, though paths are limited and can become slippery depending on weather conditions.

The castle is surrounded by a defensive ditch that was specifically designed to protect against attacks from the south and is still visible today. This ditch shows how the castle builders used the landscape to strengthen their defense line.