The remains of the Castle can be visited
Sponeck Castle

The castle ruin Sponeck, a former hilltop castle, is situated on a rocky spur near Sasbach am Kaiserstuhl-Jechtingen in Baden-Württemberg. Its special feature lies in its construction over a late antique castellum, whose remains are still visible today, showing the site's history as a strategic point on the Rhine.
History+
The site's origins date back to late antiquity, when a Roman castellum was built around 370 under Emperor Valentinian I. This facility served to secure the Rhine crossing and defend against Germanic tribes. Together with other castella in the region, it formed a network of military outposts. After the Romans withdrew and a possible use by Alemanni and Franks, the castellum fell into disrepair. It was not until after 1281 that the hilltop castle Sponeck was built on the remains of this Roman fortification by Herildebrand von Sponeck. In 1333, the castle passed to the Counts of Württemberg and served as a bridgehead to Alsace.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://commons.wikimedia.org/wiki/File:Kaiserstuhl_2012_134.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: 48.1141, 7.5839