Around 320 BC a Greek explorer from Massalia named Pytheas sailed six days north of Britain and described a place where sea, land and air blended into a jellyfish-like slush beneath a sun that never set. His lost book On the Ocean survives only in the complaints of critics like Strabo, who branded him an arch-falsifier. This episode explores how that real encounter with sea ice, fog and the midnight sun became Thule, a 2,000-year geographic ghost story.

We look at Pliny placing it on the Scythian parallel, Tacitus claiming a Roman fleet saw it, Procopius describing a 40-day polar night, an Irish monk in 825 recording clerics picking lice from their shirts at midnight, and the candidates from Iceland and Norway to Lennart Meri's 1976 theory linking Thule to Estonia's Saaremaa and the Kaali meteor crater. Then we follow ultima Thule into meta ...