Across the Andes by Frog (1977)

Explorer Walter Snetterton and his party travel to the Andes to prove his theory that frogs are able to climb mountains. Due to the Cup Final the only person willing to act as guide is an elderly - but extremely agile - old lady and as Snetterton prepares to strike camp all his men desert him for the charms of the local ladies. Snetterton is never found but the frogs manage to escape and make it to Mexico City, thus proving his theory to be right.