Altenburg castle, Cultural heritage monument in Alsfeld, Germany

Altenburg Castle is a fortress built on a hilltop in Alsfeld that dominates the town's skyline from nearly every angle. Its stone walls form a compact structure with multiple buildings arranged around a central courtyard, creating a typical medieval defensive layout.

First mentioned in 1178, the castle was held by the Aldinburg family, vassals of Fulda Abbey. Reinhard von Aldinburg sold it to Landgrave Heinrich I of Hesse in 1300; Fulda and Hessian troops took and destroyed it in 1314, and it was rebuilt. In 1647 Hessen-Kassel troops slighted the wall and burned the bergfried's interior during the Hessenkrieg.

The name Altenburg comes from the Aldinburg family, first recorded with Sifridus von Aldinburg in 1193. The free-standing Schlosskirche in the centre of the complex was built from 1748 to 1750 as a Querkirche, a Protestant hall church with the pulpit on the long side. A Christmas market is held inside the castle walls, and the small courtyard has an open-air stage.

The castle site is accessible via marked pathways from the town with multiple routes to reach the top of the hill. Daytime visits offer the best views of the surrounding landscape from the elevated position.

The medieval bergfried collapsed around 1833 and buried the sheep stall beneath it; remnants of the tower's thick walls are still visible inside the stall, and pieces of the old castle wall can be seen on the outer walls of the farm buildings.