Reading about different explorers through history, on Wikipedia, I noticed that the Greek explorer Pytheas is noted as ”discovering” northern Europe in the 4th century BC. Nothing about his finds is cited though.
However, reading that made me think about Ahmad ibn Fadlan and how he described the Norse a few centuries later. Fadlan claimed that the Norse were unhygienic, engaged in strange socioliberal rituals, etc. Did Pytheas view differ or liken Fadlan’s?
Put it simply, we cannot know for sure, since the writing of Pytheas itself has been lost, and we have to rely on the summary or quote of what Pytheas had allegedly written by later authors like Strabo and Pliny the Elder.
I suppose the following summary by Strabo (Geography 4.5.5) is the closest account OP is looking for, but it unfortunately says nothing about how hygienic / unhygienic its inhabitants were:
'The account of Thulè is still more uncertain, on account of its secluded situation; for they consider it to be the northernmost of all lands of which the names are known. The falsity of what Pytheas has related concerning this and neighbouring places, is proved by what he has asserted of well- known countries. For if, as we have shown, his description of these is in the main incorrect, what he says of far distant countries is still more likely to be false. Nevertheless, as far as astronomy and the mathematics are concerned, he appears to have reasoned correctly, that people bordering on the frozen zone would be destitute of cultivated fruits, and almost de- prived of the domestic animals; that their food would consist of millet, herbs, fruits, and roots; and that where there was corn and honey they would make drink of these. That having no bright sun, they would thresh their corn, and store it in vast granaries, threshing-floors being useless on account of the rain and want of sun' (Strabo, Geography, 4.5.5. Translation is taken from Perseus Online Edition).
References: