Germania as Rome defined it was full of settlements, I believe remains of some have been found such as that on top of Kalkriese Hill where Varus and his three legions went down. As the Romans were also building settlements in Germania, the fact that Germans were living in them and regularly trading with them might suggest they were familiar with the concept of towns.

Tacitus is clear that when the Romans went into Germania under Germanicus, they targeted German settlements as much as they could to force the Germans to battle. I would suggest that the German settlements were not as large or developed as those in Gaul when Caesar tore through the place, as I can't think of any Germans bothering to stop and defend any particular settlement against a siege like the Gauls did. On the other hand, there seem to have been significant towns or perhaps even cities in Illyria that the Romans did have to reduce the old fashioned way the Great Revolt from AD 6-9.

That said, various pressures did seem to compel Germanic tribes to start migrating. According to Caesar, groups such as the Helvetii wanted somewhere better to live and he noted they had to destroy their settlements before they moved on, which considering their numbers must have included some significant towns. Climate change, war, opposing migrations, population pressure and general restlessness seem to have motivated various large groups to move West, where the climate was both more pleasant and I suppose better for agriculture, and obviously the greatest and most prominent migrations occurred from the second century AD until the fifth century, which as we know was a huge pressure on the Roman Empire.

Well the Gauls, Dacians, Iberian Tribes and British tribes all had major settlements as we know because the Romans had to siege and capture several of them, a famous example would be Alesia. Did you perhaps mean later "barbarian" opponents of Rome?