For people interested in Antiquity, Trier has several ruins and two museums to offer. The ruins of the Imperial Baths and the Amphitheater are situated in the east, the Barbara Baths and the Roman bridge in the southwest, the Porta Nigra in the north and the reconstructed Basilica of Constantine in the east.
It is very close to the Landesmuseum, which has recently been renovated. I am pretty sure that some models have been removed, and am less sure that there used to be more mosaics. Still, the collection is interesting.
It covers almost the complete history of Trier, from the traces of the first humans to the eighteenth century. The main part, however, is dedicated to Roman history, especially to many monumental tombs from Neumagen. Made of sandstone, they are less splendid than the marble statues of Italy and Greece, but still, many of them are very impressive.
Other rooms display objects from Prehistory, from the Bronze Age, from the Iron Age, or objects related to Roman religion. There are several splendid mosaics, you will find objects illustrating the ancient economy, a small exhibition about coinage, a beautiful model of the ancient city, and a collection of Christian epitaphs. The remaining rooms are dedicated to Medieval history.
I had visited the place several times before, and was always very impressed, but this time, I sensed that something was missing; I do not know what (except for the models). Nevertheless, it is a nice place with a remarkably good restaurant. If you buy an “Antikencard”, you pay less and will have access to other monuments too.
The Diözesanmuseum is the museum of the Archbishop of Trier. Its claim to fame is a splendid fresco (more), which is sufficient to pay a visit.
Finally, there’s the strange bathhouse at the Viehmarkt. You will an impressive ruin in a large box of concrete, steel, and glass. To be honest, I liked the modern architecture better.