The story of Urashima Taro is a a folk tale that will be known by anyone who has grown up in Japan.
Once upon a time, there was a young teenage boy named Urashima Taro. He was a normal boy from the village, and was on his way to catch some fish for dinner. On his way to the river, he comes upon a bunch of small children, seemingly gathering around something. They are in such a tight circle that Urashima cannot see. His curiousity gets the better of him and he goes in for a closer look.
The children are harassing a turtle that has wandered too far from the river. "Hey!" Urashima yells, "Leave that turtle alone!" The group disperses at Urashima's shouting, most probably because he is older and bigger than any of the other children present. Urashima then picks up the turtle and takes it with him as he continues to the river.
When Urashima finally reached the river, he set the turtle free. The animal splashed happily in its native environment for a while, and then swam back to Urashima Taro.
"Thank you for rescuing me from the children," the turtle said, "In return, I can take you to the Sea Dragon's Palace on my back!"
Having never been to the Sea Dragon's Palace before, Urashima Taro agreed and the turtle took him there. As he arrived, a beautiful young woman awaited him. She was Princess Otohime, ruler of the Sea Dragon's Palace. After hearing of the turtle's rescue, the princess welcomed him and Urashima Taro became a most favored guest at the palace. He was treated to a grand feast, and elegant dances and songs by the princess herself.
"You're welcome to stay as long as you like," the princess said, and Urashima took her up on that offer. Every day was the same as when he first arrived, filled with lots of delicious food and the songs and dances of Princess Otohime. The days became weeks, which turned into months, and soon Urashima forgot how long exactly he had been at the Sea Dragon's Palace.
Despite the fact that the Palace was such a wonderful place, Urashima found himself missing his home village. He wondered how his friends were doing, and he missed his family very much. He told the Princess that he would like to return home. She was sad that he had chosen to leave, but agreed that perhaps visitng home would be a good idea. She presented him with a present before he left. It was a simple box, decorated with corals and pearls.
"Consider this a souveneir of your stay here. When you look upon this box, hopefully it'll remind you of the fun that you had here. But whatever you do, you mustn't open this box," she said as she presented him the gift.
And with that, Urashima Taro once again rode the back of the turtle and headed back to his village. However, once he got there, everything seemed different. His house was no longer there, and he couldn't recognize anybody that was walking along the streets. He suddenly felt very lonely. The only thing that he had was the box that the princess had given him, and he was so distraught that he forgot her warning and opened it.
As he opened the box, there was a popping sound and a cloud of white smoke. After blinking and coughing the smoke away, he realized that he suddenly felt much older. Urashima looked down upon himself and realized that indeed he had become an old man.
And that concludes our tale.
There are numerous ways that this story is told, as is the case with many folk tales. In some versions, there is no Princess Otohime, but Urashima meets the Sea Dragon himself. In other versions, the Princess says that Urashima can return to the palace only if the box is unopened, or she promises to marry Urashima if he returns with the box unopened.
It has been spectulated by some that the Urashima Taro tale may not be totally fiction. While the parts about an underwater palace and riding on the back of a turtle are most likely made up, some people say that there is a hint of truth. For instance, Urashima Taro may have been a fisherman who was caught in a storm and wound up somewhere in Micronesia (the currents happen to flow that way). In that kind of tropical climate, the seasons would not be well defined, it would be easy to lose track of days. However, no one has been able to actually prove anything either way.