Schwarzenberg Castle, Medieval castle in Plettenberg, Germany

Schwarzenberg Castle is a ruined hilltop castle near Plettenberg in North Rhine-Westphalia, set on a wooded ridge above the Lenne valley. The surviving stonework includes sections of curtain wall, tower foundations, and parts of the residential wing built across different periods.

Eberhard I of the Mark began Schwarzenberg Castle on 2 October 1301 under a alliance with Count Ludwig of Arnsberg, to secure the county's southern border after the Archbishop of Cologne redeemed Waldenburg in 1300. Count Engelbert III of the Mark bought out Arnsberg's rights in 1352 and had the castle expanded from 1353, keeping it as a residence; a fire destroyed it in the 19th century.

The castle displays military architecture from the Middle Ages with features built over several centuries, reflecting how the noble residents lived here. The structures and remains show how important this place was for regional power and family traditions.

The ruins are reachable from Plettenberg on foot via marked trails through the forest, making them a good destination for a short walk. The ground is uneven in places, so sturdy footwear is a good idea.

The site carries two separate forms of protection, one for its above-ground remains and one for what lies beneath the surface, which is rare for a site of this size. Finds from the ground have revealed details about daily life here that the visible walls alone cannot show.