Burgruine Tachenstein, Castle ruin in Riedenburg, Germany.

Burgruine Tachenstein is a castle complex near Riedenburg with a surviving tower roughly 10 meters tall and foundation remains of other buildings on a ridgeline. The site sits at about 450 meters elevation and still shows visible sections of its defensive walls and former ditches.

The site was built between 1170 and 1180 and is first documented in 1189. In 1329 the castle passed to Bavarian dukes and later changed hands several times through marriages and inheritance disputes.

The ruins display regional stone construction techniques typical of medieval fortifications in this area. Visitors can observe these building methods directly while exploring the remaining walls and structures.

The ruin sits on a southeast-facing spur of the Jägerberg at about 440–450 m, directly west of Riedenburg's old town, with the Altmühl flowing 90 m below. Access was historically only on foot or with animals, not with wagons; today paths are unmarked, so wear sturdy footwear. The tower entrance is 6.5 m above ground and the site is fully exposed to weather.

The castle was a contested property among different noble families and changed hands through complicated inheritance arrangements. These conflicts ultimately led to the site's decline and explain why only fragments survive today.