The remains of the roman Castle can be visited
Roman Castle Heidenstock

The small fort Heidenstock was a Roman military camp on the Upper Germanic-Rhaetian Limes on its section 3 (Taunus, between watchpost 55 and watchpost 60 (presumably around 58, not preserved)). The fort is located about 5 km from the Saalburg near Arnoldshain, in the municipality of Schmitten, in the Hessian Hochtaunuskreis.
Today, it is only accessible on foot, on a Taunus circular hiking trail from Sandplacken along the Klingenkopf, where there is another small fort. It is surrounded by dense spruce forest.
Fort+
Only the foundations of the stone enclosure (quartzite fragments) remain. Although heavily decayed, it is still recognizable. The fort had only one gate, in the north. Relics of the palisade ditch in front of it were still visible in the 19th century, which is no longer the case today. Research has shown that a fireplace was present, because large quantities of burnt debris mixed with clay were found.
Historians assume that the garrison consisted of a smaller guard detachment (approx. 20 men), which was seconded from the two larger forts Kleiner Feldberg and Saalburg.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://commons.wikimedia.org/wiki/File:Kleinkastell_Heidenstock_4.jpg
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: 50.2538, 8.5129