The paperback is coming out this month for a mere $60. :^)
Pytheas’ original text did not alas survive, except as quotes in other authors. Modern commentary on it range from “it never happened” very nearly to “he discovered America”.
https://www.amazon.com/s?k=pytheas
I went down the rabbit hole about Pytheas.
Seems that his almost contemporaries (300 BC) called him a fraud. Scorned as a common person. He was perhaps driven by money to a degree (to find the tin and amber sources), but was mostly a scientific explorer. He had some device to measure latitude, and his measurements confirm where he said he was. (North-south anyway). So it might have been Iceland (which he called Thule), or it was Norway. He even got to the “congealed sea” (frozen/slush).
Pliney and others later on also referenced his work, and based on later discoveries figured Pytheas as reliable.