Watch: An Incredible Viking Voyage—Made Entirely of Paper | National Geographic

I am old, but I remember long ago when we Norsemen ruled the sea. As our northern kingdom expanded, the secret of our success lay in how we built our fearsome longships.

Imagine a young boy named Harold who yearns to see the world. His father is a shipbuilder; he shares the secret to finding the right trees. He looks for a tall, straight trunk for the keel, and clanking—then he finds the ship's frame hidden inside the curved link. The keel is hewn from the center of a trunk and laid down first. Other logs are split for the long sleek planking, which is attached to the keel, and the inner framework is added last. After many months, it's finished—a swift, light, and flexible masterpiece.

As far out grows, so does his reputation for building good ships. We use the ships for exploration, trade, warfare, and even burials for honor. It's the beginning of a long journey, and his first voyage is a raid on the Irish coast. The raiders return home with goods and many slaves.

Years later, Harold takes his men around the Iberian Peninsula to sail up the Guadalquivir River. From there, they attack the city of Seville. The atmosphere is tense, and it is here that morale grows.

"Come with me now. I've invited Harold to my home, for I live in the realm of Asgard. My name is Odin, father of the Nordic gods. Now I will hear Harold's story from his own lips here in the halls of Valhalla."