Burg Arnesvelde, Medieval castle ruin in Ahrensburg, Germany.

Burg Arnesvelde is a medieval castle ruin on the eastern edge of the Hopfenbach Valley in Ahrensburg, Germany. What remains today are earthen ramparts, ditches, an oval mound with traces of ring structures, and a western ramp that once led to a former pond.

The castle was founded in the second half of the 11th century by Count Heinrich I of Hamburg to control the northeastern part of Stormarn and to guard the trade route between Hamburg and Lübeck. Over the following centuries it lost its role as power shifted across the region.

The name Arnesvelde comes from the neighbouring village of Ahrensfelde, first mentioned in a 1195 charter when Count Adolf III of Holstein gave the village to the Hamburg Cathedral Chapter. The gift was never carried out after King Waldemar II of Denmark conquered the land in 1202. Ahrensburg's coat of arms shows the castle in its upper field.

The site is accessible along maintained walking paths fitted with information boards about the ruins. Spring through fall offers the easiest walking conditions and the clearest views of the earthen features.

The castle's name comes from the nearby village of Ahrensfelde, not from a noble family. Ahrensburg's coat of arms shows the castle in its upper field. The town's own name refers back to the ruin in the Forest of Hagen, whose remains were likely demolished around 1575 when Peter Rantzau built Ahrensburg Manor.