Charles F. Muntz has been accused of fabricating the skeleton of a giant bird he had claimed to have discovered in Paradise Falls in South America. Muntz vows to return there to capture another giant bird alive.
Best childhood friends, Carl and Ellie eventually get married begin to grow old together. Unable to have any children, they repeatedly pool their savings for a trip to Paradise Falls, but end up spending it on more pressing needs. An elderly Carl finally arranges for the trip, but Ellie suddenly becomes ill and dies, leaving him alone and lonely.
Years later, 78-year old Carl still lives in the house, now surrounded by urban development, but he refuses to sell. He ends up injuring a construction worker over his damaged mailbox. As a result, he is evicted from the house by court order and ordered to move to a retirement home. However, Carl comes up with a scheme to keep his childhood promise to Ellie: He turns his house into a makeshift airship, using thousands of helium balloons to lift it off its foundations. He then floats his house to Paradise Falls.
- Director Pete Docter and a select group of artists visited Canaima National Park in Venezuela to witness the tepuis firsthand, and to collect the sketches, photographs, and video that would later be used by art and technical directors as reference in creating their own "Lost World."
- The name is likely based on Angel Falls, which is the highest waterfall in Venezuela.