The Cathedral can be visited
Cathedral Treves

The High Cathedral of Saint Peter in Trier, Germany's oldest episcopal church, is the mother church of the Diocese of Trier. With a length of 112.5 meters and a width of 41 meters, it shapes the cityscape of Trier and has been part of the UNESCO World Heritage since 1986.
History+
The cathedral's origins trace back to Roman times, built upon the foundations of a Roman residential house from the 2nd and 3rd centuries. Under Bishop Maximin (329–346), a basilica was erected on this site, which expanded into one of Europe's largest church complexes. Around 340, the Square Building, forming the core of today's cathedral, was constructed.
Source: Wikipedia · Licence: CC BY-SA 4.0
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: 49.7562, 6.6438