Finn remembers the stories his grandfather told him about a place where the ocean meets the sky, where whales and jellyfish soar and birds and castles float. Now that his grandfather is gone, Finn knows the perfect way to honour him. He'll build a boat. He'll set sail. He'll find this magical place himself!

Mae Gwern yn cofio gwrando ar ei daid yn adrodd straeon am fan lle mae'r môr yn cwrdd â'r awyr, lle mae morfilod a slefrod yn hedfan ac mae adar a chestyll yn arnofio. A'i daid bellach wedi mynd, er mwyn cofio amdano, mae Gwern am adeiladu cwch a dod o hyd i'r man hudol hwnnw. Ac ar y daith, efallai daw Gwern o hyd i rywbeth ...