Heilgenberg is a 393 m (1,289 ft) high hill close to the town of Felsberg-Gensungen in North Hesse.

Archbischop Conrad I constructed strong fortification on the Heiligenberg between 1180 and 1186 as protection against Louis III, Landgrave of Thuringia.

Shortly after the building of the castle there was bitter fighting, because the fort lay strategically between Felsberg, Gudensberg, and Melsungen, and combined they threaten the strongly-fortified Fritzlar, which was the centre of the Electorate of Mainz power in North Hesse and the geographical heart of the Landgraviate of Hesse.

In 1193 a knight named Heinrich von Heiligenberg is documented, who was probably an offspring of the nobles from Uttershausen (close to Wabern), and from 1196 until their demise in 1263, the family Isfried von Heiligenberg were castellans (German: Burgmannen) of the castle and had to protect it in the name of Mainz.

The landgrave ordered that the monks should pray for the castle's soul at least one a week in the church on the hill.

In 1952 a castle gate with a bell was installed and dedicated to the displaced people of World War II.

In 2002 a sculpture trail – Ars Natura- was initiated; local artists have put various pieces of objet d'art along a path around the Heiligenberg.