Algersdorf Castle or Alt-Eggenberg Castle is located in the town of Algersdorf in the 14th district of Eggenberg and is located a little north of Eggenberg Castle on Baiernstrasse.
The building in its current form, which dates back to the 15th century, serves as a residential and administrative building. The former fortifications are no longer recognizable today.
In the 14th century, the estate seems to have lost its importance as a noble residence and become a farm.
Up until the 20th century, it was believed that Algersdorf was the ancestral castle of the Princes of Eggenberg. It was therefore also known as Alt-Eggenberg from the 19th century. Only archaeological investigations cleared up the error. In 1754, Algersdorf was uninhabited and in need of repair.
Algersdorf Castle is a stately three-story building with an almost square floor plan, surrounded by tall trees. Its appearance has not changed significantly since the Vischer engraving of 1680. The front faces east, towards Baiernstrasse. It is dominated by two protruding tower-like corner projections. These originally had tent roofs, but were replaced by late Baroque mansard roofs towards the end of the 18th century. The facades are smoothly plastered. Those of the projections are discreetly decorated in the panel style. The individual floors are visually separated by continuous cornices and plaster bands. The simple round-arched stone portal in the middle of the building dates from the 17th century, the sheet metal-clad gate wing from the end of the 18th century. The rectangular inner courtyard is decorated on three sides with three-storey arcades from around 1580.