The Goddess of Atvatabar / Being the history of the discovery of the interior world and conquest of Atvatabar

A polar expedition breaches the ice and discovers an interior world accessible through a polar gulf. The explorers voyage across an inner ocean, meet advanced inhabitants, learn their language, and are escorted to cities and palaces where a supreme goddess rules. They witness religious rites including twin-soul installations, political intrigue and moral crises centered on the goddess, and escalating conflict that leads to battles, arrests, and a leader's death. Scientific curiosity, cultural exchange, and warfare culminate in victory, reincarnation themes, and a royal marriage and coronation that seal alliances between the visitors and the interior realm.