Horst is a half-ruined Flemish Renaissance castle set on the edge of a lake, 6km south of Aarschot.

The origins of the castle are unclear. A "castellum Rode" is mentioned in 1100, but the name Horst does not show up until 1268. Like most late medieval castle built in a plain, Horst castle was constructed as an irregular polygon surrounded by a wide moat. Nevertheless, all the feudal castle but the dungeon burnt down in 1489 during the war between Emperor Maximilian of Austria and the citizens of Leuven.
A Renaissance-style castle was rebuilt in the late 16th century, keeping the original layout. Horst castle was only inhabited until the mid-17th century, and as a result there is no furniture inside nowadays. The castle passed by inheritance to the Merode family in 1712, then to the Thiennes de Lombize,Ribaucourt, then to the Count of Hemricourt de Grunne in 1922, and finally to the Count Cornet d'Elzius in 1972.

The locals say the ghost of the lord of Rode comes back everyday at midnight in a carriage pulled by six wild horses. The soul of the legendary 15th century lord cannot find rest for having murdered a priest. Two versions of the story exist. The first one says that the priest had started the mass in the castle before the arrival of the lord, and this latter, angered by the priest's disrespect, cut his throat on the spot. The second version has it that the priest had had an affair with the beautiful wife of the lord.