Complex sentence: The voyages, or "immrama", are tales of sea journeys and the wonders seen on them that may have resulted form the combination of the experiences of fishermen combined and the Other World elements that inform the adventures.
Split into simpler sentences: The voyages, or "immrama", are tales of sea journeys and the wonders seen on them. These probably grew from the experiences of fishermen combined with the Other World elements that inform the adventures.