Cultural center
Museum
The Fortress can be visited
Fortress Mainz-Reduit

In Wiesbaden-Mainz-Kastel, the Mainz-Reduit Fortress once served as the redoubt barracks for the Kastel bridgehead of the Federal Fortress of Mainz.
History+
Between 1830 and 1834, the fortress was constructed by Austrian pioneers following plans by Engineer General Franz Scholl, under the direction of Engineer Captain Christoph von Pittel. It was built as part of the reinforcement of Kastel's main ramparts, which took place from 1828 to 1830. The two-story barracks are solidly built and feature crenellated walls for close-range defense. Its landward-facing front is slightly bastioned. The foundation was laid on a pile grillage of 1800 oak piles.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://de.wikipedia.org/wiki/Datei:Bundesfestung_Mainz_Kastel.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: 50.0065, 8.2813