The remains of the Castle can be visited
Hopfen Castle (Ruin)

On a hill above the Füssen district of Hopfen am See in Ostallgäu lies the Hopfen Ruin, one of the oldest stone castles in the Allgäu region. Its well-preserved wall remnants offer an insight into high medieval architecture.
History+
The exact origins of Hopfen Castle are not entirely clear. It may have served as a retreat for the Augsburg anti-bishop Wigolt as early as 1078 during the Investiture Controversy. Between 1172 and 1191, the complex was the seat of a Welf ministerialis family who named themselves after the castle. Subsequently, it passed into the possession of the Prince-Bishopric of Augsburg and served as the official residence of the Füssen provost until 1322. With the construction of the Hohes Schloss in Füssen, the castle lost its significance and began to decay.
Source: Wikipedia · Licence: CC BY-SA 4.0
This description draws on the facts documented in the linked Wikipedia article; Wikipedia content is licensed under CC BY-SA 4.0. Wording and editing: Mobile History.
Location: 47.6105, 10.6714