Uster Castle was built probably around 1200 by the House of Rapperswil. After the Appenzell wars Hans von Bonstetten concluded a pact with Zürich, and became a citizen of the city of Zürich respectively claimed the so-called Burgrecht in 1407. From that moment, the castle in time of war could be strengthened by a Zürich garrison. As an Austrian vassal, Zürich guaranteed a neutral status to the Bonstetten family, particularly during the Old Zürich War when the neighbouring town of Greifensee was besieged and destroyed by Old Swiss Confederacy marauders; the bodies of the defenders were buried at the Uster church.
In 1492 a fire destroyed the castle. The owners changed the following centuries many times. In 1852 the castle became the seat of the district administration, and the tower was used as a prison. In the same year the castle was rebuilt, again, and a restaurant opened. Since 1995 the castle houses the private boarding school, and the former restaurant Burg was rebuilt in a steakhouse in 2009.
From the first construction phase, the lower section of the tower, up to the level of the upper floor of the today's boarding school's building around the tower base, is preserved, but never was scientifically examined, as well as the surrounding area of the plateau. The core of the present tower measures about 11 metres.References:
The Broch of Gurness is an Iron Age broch village. Settlement here began sometime between 500 and 200 BC. At the centre of the settlement is a stone tower or broch, which once probably reached a height of around 10 metres. Its interior is divided into sections by upright slabs. The tower features two skins of drystone walls, with stone-floored galleries in between. These are accessed by steps. Stone ledges suggest that there was once an upper storey with a timber floor. The roof would have been thatched, surrounded by a wall walk linked by stairs to the ground floor. The broch features two hearths and a subterranean stone cistern with steps leading down into it. It is thought to have some religious significance, relating to an Iron Age cult of the underground.
The remains of the central tower are up to 3.6 metres high, and the stone walls are up to 4.1 metres thick.