The church can be visited
St. Stephan Church

The Catholic Church of St. Stephan in Mainz-Gonsenheim is a house of worship, distinguished by its Neo-Gothic architecture and size. It is considered the largest rural church in Rheinhessen and is therefore often referred to as the “Rheinhessen Cathedral.”
History+
The first documented mentions of St. Stephan Church date back to 1401. The church received its current Neo-Gothic appearance primarily through works completed in 1906. At that time, the nave was extended to over 62 meters, and the two almost 60-meter-high bell towers were erected. Between 1964 and 1967, modern stained-glass windows by the artist Heinz Hindorf were installed.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://commons.wikimedia.org/wiki/File:Gonsenheim5.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: 49.9992, 8.2084