The (Celtic) Castro culture of Spain, dating from the Bronze Age until the final Roman conquest in the 1st century BCE boasted cities that were quite large in ancient terms. Apart from the saunas that were mentioned in other posts, they also had a fair level of plumbing with drains, wells for drinking water and because oppida were built on the top of hills, the rainwater runoff would have washed away unpleasant stuff; in fact, these oppida actually show quite high degree of sophistication. The domestic areas were divided separately into various work, living and storage spaces that were built around a courtyard which often had drains and freshwater wells. Most archaeologists will tell you too, that the best place to find the “rubbish” is outside the city walls or fortifications, i.e. in the ditches. The people had the good sense not to create squalor in their own backyard, literally. Of course, the Romans were also known for their plumbing skills, and they even had Cloacina, the goddess of the sewer, surprising as that may seem to us today.
Various Celtic peoples were noted by ancient writers for the cleanliness and the Irish Brehon Laws from a millennium ago also covered personal hygiene and the right to free healthcare, the latter still unavailable to many people in our so-called “civilised” modern world.
Another historical falsehood that has been promulgated thanks to television and films is that they all had rotten teeth, this quite unlikely as sugar was unknown/unavailable in Western Europe at least. Their teeth would have been worn from eating stone-ground bread, but they may not have suffered from the dental problems that modern people suffer from.