Burg Alt-Sternberg, Medieval castle ruins in Dörentrup, Germany

Burg Alt-Sternberg is a medieval fortress ruin on Mühlingsberg near Dörentrup with a three-part defensive structure consisting of outer walls, a lower bailey, and a main castle section. A moat system originally surrounded these areas, creating distinct boundaries and protection against attacks.

Alt-Sternberg was in use from the late 11th century until the early 13th century, when it was abandoned; its successor, Burg Sternberg, lies about 1.5 km to the southeast. No written sources name its builders. Otto Weerth's 1908 excavation of the roughly 1,000 m² main castle found cellar pits of five houses, Pingsdorf pottery, iron tools, a glass ring, pig bones, a coin of Henry of Champagne (1192–1197) and a Soest halfpenny.

The name Sternberg comes from the site's position on a spur of the Mühlingsberg. The castle was probably used at the same time as nearby Burg Sternberg before being abandoned. Visitors can see the preserved ramparts and ditches that mark the former three-part layout.

This is an archaeological site that can be viewed from walking paths, where visitors can see the moats and wall foundations. The location sits at 300 meters elevation and is best visited in dry weather, as muddy ground conditions can make access difficult after rainfall.

Excavations uncovered everyday objects that reveal how residents lived and worked, including pottery, iron tools, and animal bones. A particularly rare glass ring was found, suggesting that people of some wealth also lived at this site.