a clan of Mountain giants believe a human mage can lead them to victory against the slightly superior Mist Giants of a neigboring mountain…their ancient cave drawings (think Bayern Tapestry on cave wall) tell them so…
"Many strange things may be seen in the Great Swamps, not all real. But I tell you, there was a ship and it was real! Well it was old and all sails torn and had many holes in the hull... but anyway it was hundreds of miles from the Sea! How it came to be there, I can only wonder..."
(If it is not a hallucination, may be inhabited by wererats.)