Auenstein Castle is a castle in the municipality of Auenstein in the Swiss canton of Aargau. It was created by converting a medieval castle. The castle was probably built in the 13th century on behalf of the Lords of Gowenstein and was first mentioned in documents in 1307 as the property of the Lords of Rinach. During battles between the Habsburgs and the Swiss Confederates in 1389, the Bernese stormed the castle and burned it down. The complex was not rebuilt and remained a ruin until modern times.
As the ruin was also linked to the rule over the village of Auenstein, the uninhabitable building changed hands several times. Albrecht von Rinach sold the ruin to Heinrich Hasfurter from Lucerne in 1465. In 1487, the ruin became the property of Hans Rudolf von Luternau, who sold it on just four years later to the von Mülinen family from Brugg, who already owned the nearby Kasteln Castle. General Johann Ludwig von Erlach bought the ruins in 1648, which were sold to the city of Bern by his descendants in 1732.
In 1803, the complex came into the possession of the newly founded canton of Aargau, which then sold it to private individuals. In 1858, the ruins were made habitable again and converted into a castle by adding additional floors with an apartment and kitchen on top of the old foundations; an extension was added in 1928. The castle is still privately owned today.