One fine day a young fisherman named Urashima Tarō was fishing when he noticed a small turtle being tormented by some children. Tarō saved it and let it go back to the sea. The day after a huge turtle approached him and told him that the small turtle he had saved was the daughter of the Emperor of the Sea, who wanted to see him to thank him. The turtle magically gave Tarō gills and brought him to the bottom of the sea, to the Palace of the Dragon (Ryūgū-jō). There he met the Emperor and the small turtle, who was now a lovely princess.
Tarō stayed there with her for a few days, then he was caught by the desire to go back to his village and see his aging mother, so he asked her permission to leave. The princess said she was sorry to see him go, but wished him well and gave him a mysterious box which she told him never to open, for whatever reason. Tarō grabbed the box, jumped on the back of the same turtle that had brought him to the Palace, and soon was home.
But everything had changed. His home was gone, his mother had vanished, the people he knew were nowhere to be seen. He asked if anybody knew a man called Urashima Tarō. They answered that they had heard someone of that name had vanished at sea long ago. He discovered that 300 years had passed since the day he had left for the bottom of the sea. Struck by grief, he absent-mindedly opened the box the princess had given him. Out of it came a cloud of white smoke. He suddenly aged, his beard grew long and white, and his back bent. He was now a very old man. And from the sea came the sad, sweet voice of the princess: "I told you not to open that box. In it was your old age …"
As always with folklore, there are many different versions of this extremely famous story. In one, for example, after he turned into an old man he took the body of a crane, in another he ate a magic pill that gave him the ability to breathe underwater. In another version, he is swept away by a storm before he can rescue the turtle.
A shrine on the western coast of the Tango Peninsula in northern Kyoto Prefecture, named Urashima Jinja, contains an old document describing a man, Urashimako, who left his land in 478 A.D. and visited a land where people never die. He returned in 825 A.D. with a Tamatebako. Ten days later he opened the box, and a cloud of white smoke was released, turning Urashimako into an old man.
The story influenced a number of works of fiction and movies. Among them are Urusei Yatsura, Love Hina, Doraemon, Cowboy Bebop and RahXephon. It is retold in and used as the basis for the short story “Another Story” by Ursula K. Le Guin, published in her story collection A Fisherman of the Inland Sea, named for the character of this story. Urashima Tarō himself is a character in the video game Ōkami.
The oldest known animated adaptation of the tale premiered in 1918.
During the 1970s, VARIG, a Brazilian airline, used him in a series of commercials, with the turtle bringing him to Brazil. After a while, he enjoys his stay, but grows old and longs to return to his home in Japan, so a woman (presumably the princess) gives him a box with a airplane ticket home, which when he opens also becomes much younger.
The Voyage of Bran is also similar to this story.
In English there is the tale of the ancient Briton King Herla, from De Nugis Curialium. King Herla spends three days in the dwarf kingdom, and returns only to discover that many centuries have elapsed.
In India, the Srimad Bhagavatam describes how King Kakudmi and his daughter Revati spend a short time visiting Brahma and return home to find 27 catur-yugas (see yugas or Ages of Man) have elapsed, and not only everyone they knew is dead, but even their names have been forgotten in the mists of time.
Intriguingly, King Kakudmi and his daughter Revati are inhabitants of Kusasthali, a kingdom beneath the ocean. Note the similarity of the reference to the Dragon King and his daughter, who inhabit the Palace of the Dragon (Ryūgū-jō), also located in the ocean depths.