The Castle can be visited
Frankenburg Castle

On a small mountain spur above the town of Bad Frankenhausen, on the southern edge of the Kyffhäuser in Thuringia, stands the Frankenburg, a High Medieval fortification. Its location near former salt extraction facilities makes it a historical testament.
History+
The origins of the Frankenburg stretch far back. Even before the first documented mention of Frankenhausen as an oppidum in 1219, the Counts of Rothenburg erected an initial castle complex at this site. This was already referred to as "Frankenhaus" in 998, from which the current place name is said to be derived. In 1340, the fortification passed into the possession of the Counts of Schwarzburg and was subsequently called "Haus". Later, in 1381, it bore the name "Oberburg" and from 1592, "Alte Burg".
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: Roland Neubert, Halle (Saale)
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: 51.3608, 11.1043