Nonki na Tousan Ryuuguu Mairi(1925)

One of the first examples of the tale is Hakuzan Kimura's Dreamy Urashima (Nonkinatousan Ryugu Mairi, 1925), in which a lazy man wakes up from his sleep and heads off to the seaside to spend the day fishing. There is a brief live-action shot of the sea swelling before the film returns to its animated fantasy world when a beautiful girl appears on the beach and lures him into the waves, transforming into the legendary turtle and carrying him beneath the surface to an undersea kingdom of fish and squid. Here he is welcomed by a bevy of kimono-wearing lovelies who lead him to a stately court full of musicians and dancers. As a ballerina pirouettes on the palace floor in front of him, he is plied with alcohol and handed a small gift box, before being escorted to a giant scallop shell that rises through the water taking him back to the surface. When he returns home, he finds he has aged so much that his wife and son no longer recognise him. He opens the gift box and a hideous demon springs from it and squashes him beneath its fists, at which point the man wakes up, and realising that the events of this story have all been a terrible nightmare, hurries out to work, alerted to the potential dangers of a life spent in idle daydreaming.

(Source: midnighteye.com)