Trier lies in the Moselle wine region along the banks of the Moselle River and is the oldest city in Germany. Founded by the Romans, it contains several well-preserved Roman structures like the Porta Nigra gate, the ruins of Roman baths, an amphitheater just outside the center and a stone bridge over the Moselle River. Among Trier’s many Catholic churches is Trier Cathedral of St. Peter. The UNESCO information can be read here.
Interior of Constantine I's throne room above, the largest single standing structure from the 4th Century.
The amphitheater, above and below ground, dating to the 2nd Century.
The Porta Nigra gates, 180 A. D. look to be in pretty good shape, all things considered.
Trier is full of UNESCO World Heritage sites. You can see them all here.
Cathedral of St. Peter with the entrance seen below