Picturesquely situated along the Ahauser Aa, the moated castle Haus Horst rises from its castle grounds as one of Heek's most important sights. The castle affords a view of the historic manor house with its well-tended grounds.
The simple rectangular brick building with seven window axes and a high hipped roof was built around 1580. As the noble residence of the married couple Jakob von Keppel, Burgmann zu Nienborg and Elsebe von Münster, Haus Horst was given the secondary name "Haus Keppelhorst". A conspicuous reconstruction then took place for the first and last time in 1674 under the new owner Heinrich Bruchhausen, the secretary of the Münster bishop Bernhard von Galen.
In 1881, the castle went to the former banker and art collector Hugo von Hartmann. Since then, there have been further changes of ownership through marriage and inheritance, so that the estate is still privately owned by the noble family today. In recent years, Haus Horst has been completely restored on the outside and fitted with new roofing and central heating.