The Schönborn bastion is a rebuilt blockhouse as part of the former Federal Fortress Reduit (Mainz-Kastel) on the right bank of the Rhine at Mainz Fortress.
The building was named after the builder of the former Mainz ship bridge built after the Thirty Years' War, Archbishop of Mainz Johann Philipp von Schönborn (1605-1673).
The bastion of Schönborn was built as an outwork at the same time as the reduit erected between 1830 and 1834. It served to provide additional protection for the south-eastern flank of the fortification and ship's bridge. At the same time, from 1861 it was briefly a landing stage for the train boats of the Royal Railway Directorate Frankfurt, which served the traffic between Mainz and the Kasteler station of the Taunus railway before the completion of the Mainz southern bridge for the onward journey to Frankfurt.[
Damaged during World War II, the facility was restored in the 1950s.[3] In 1998 the entire area of the Reduit was acquired by the local history association "Gesellschaft für Heimatgeschichte Kastel e.V. (GHK)" and has been further developed since then. Since 1999, a restaurant with a terrace has been in operation in the Schönborn bastion, as well as the Kasteler beach in the summer months, with a panoramic view of the city of Mainz across the way.
On the first floor of the building is the so-called raftsmen's room, a rafters' museum dedicated to this old profession with numerous exhibits. The profession of raftsman had a tradition in Kastel that went back more than 400 years. Tree trunks brought over the Main from the Bavarian Steigerwald and the Odenwald were rebundled here with regional timber and then carried further down the Rhine.
Source: Wikipedia