Heiligenburg Castle, Medieval castle ruins in Gensungen, Germany

Heiligenburg Castle is a ruined hilltop fortress on the 393 m basalt cone of the Heiligenberg above Gensungen. Archbishop Konrad I of Mainz built it between 1180 and 1186; after destructions in 1232 and 1273 and a smaller rebuild from 1401 to 1403, only the tower, gate and wall remnants survive. The tower is accessible as a viewing platform.

Archbishop Konrad I of Mainz built the castle between 1180 and 1186 against Landgrave Louis III of Thuringia, not Hesse. Its position between Felsberg, Gudensberg and Melsungen threatened Fritzlar, the centre of Mainz power in North Hesse. Conrad of Thuringia destroyed it in 1232; Mainz castellans rebuilt it in 1247, and Landgrave Henry I of Hesse destroyed it again in 1273. From 1401 to 1403 Landgrave Hermann II built a smaller castle, which passed to Eppenberg Charterhouse in 1471.

The hill's name comes from one of Hesse's oldest churches, and a bell clapper found in excavations points to a chapel on the summit, documented in the 15th century as a mountain chapel. Landgrave Louis II transferred the castle to Eppenberg Charterhouse in 1471, obliging the monks to pray there weekly for his soul. A bell was dedicated in the castle gate in 1952 to Germans displaced after World War II, and a rock festival is held on the site once a year.

The path to the top is moderately steep and goes through forest, so sturdy footwear is a good idea, particularly when the ground is wet. Arriving earlier in the day gives more time to explore the ruins without crowds.

The hill itself is not an ordinary hill but an ancient volcanic neck from the Miocene epoch, where softer rock eroded away over millions of years and left only the hard basalt core standing. This makes the site one of the few places where a medieval ruin sits directly on top of a geological formation far older than any human presence in the area.