Photo credit: Berthold Werner Wikimedia Commons
Just 45 minutes on the train (with a fare of 8.40 euro) from Luxembourg City is Trier, the oldest city in Germany, and the birthplace of St Ambrose. We entered via the Porta Nigra, reckoned to be the best preserved Roman city gate, walked down to the the Hauptmarkt and visited the Cathedral Church of St Peter. Unfortunately, the Liebfrauenkirche is currently closed for works. I have some photos, but unfortunately the (massively annoying) internet connection here in Luxembourg will not let me upload them to flickr so I have found the above at Wikimedia.
An amazing building is the Aula Palatina or Basilica of Constantine which is well preserved and is now used for the Evangelical Church Community. Again, here is an image from Wikimedia:
Trier is on the Moselle river: during the train journey, we passed many vineyards. For lunch we both chose Wiener Schnitzel and shared a bottle of very reasonably priced local wine at a pleasant hostelry in the centre of town. I tried to pronounce my fairly modest German as well as possible - it was good to have a chance to practice.