The church can be visited
Cathedral St. Peter und Paul

The Cathedral of St. Peter and Paul in Brandenburg an der Havel is a historic church building. It is often referred to as the “Cradle of the Mark” and is considered the “Mother of all churches in the Mark Brandenburg”.
History+
In the winter of 928/929, Saxon-Christian troops under Henry I conquered the main Slavic fortress of Brandenburg. This laid the foundation for the establishment of the Diocese of Brandenburg by Emperor Otto I in 948 (or 964). An initial cathedral church, begun after the conquest of Brandenburg, was lost during the Great Slavic Uprising of 983. The construction of the current cathedral began with the laying of the foundation stone on October 11, 1165. Originally planned as a single-nave fortified and missionary church, the cathedral was later redesigned into a two-towered cathedral, with the south tower remaining unfinished. It is the first building in the Mark Brandenburg constructed entirely of unplastered brick.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: https://commons.wikimedia.org/wiki/File:Dom_brb_2013.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: 52.4153, 12.5676