I must be slipping if you're still reading!
      Once upon a time, there lived a king with twelve beautiful daughters who each slept in 12 beds in one large room together.
      But he had a big problem. Though he kept his daughters under lock and key every night, in the morning they were tired and their shoes were worn as if they spent the entire night dancing. The king had had his servants search their room but they could find nothing to suggest the princesses were getting out.
     The king got so desperate that he finally offered that anyone who could figure out the mystery of how the princesses got out to dance would get to marry the princess of his choice. However, if he could not figure it out in three days, he would be executed.
     Many men tried but failed and were executed. Then one day, a man walked towards his home from battle wounded and saw an old woman begging by the side of the road for food. The man didn't have much but kindly offered her half his meal.
     At his kind gesture, the old woman told him about the challenge for the princesses. She gave him some advice, saying, "Do not accept the wine the princesses give you. Pretend to fall asleep. And wear this so that you can follow them."
     That said, she pulled out a long cloak and told him that when he wore it, he would become invisible. He thanked the old woman then went to the palace to accept the challenge.
     That night, the eldest princess brought him a goblet of wine. He pretended to drink it then laid down and pretended to sleep. When the princesses thought he was sound asleep, they dressed themselves in beautiful ball gown and did each other's hair, laughing as they did so.
     When they were ready, the eldest princess tapped on her bed's headboard three times and a passage opened for the princesses. They descended into the tunnel, eldest to youngest.
     The man threw on the cloak and followed the princesses down the tunnel and through three forests: one of gold, one of silver, and one of jewels. He broke off a branch of each one as proof.
     Now, it's fair to say that the youngest princess was suspicious. She kept relaying her bad feelings to her sisters but the eldest princess always quieted her.
     The man followed the princesses to a beautiful lake where they were rowed across by 12 princes to a castle where they danced all night long. The man followed the 12 princesses all three nights except that on the third night, he grabbed a goblet from the castle.
     On the fourth morning, the king asked if the man had solved the mystery. He explained the whole story and showed the branches of gold, silver, jewels, and the goblet as proof. The king was pleased and asked which princess he could want.
     In one version, he married the eldest princess. In the other, he declares he'd rather the princesses marry the princes they dance so gracefully with. He is invited to the wedding which goes on for 12 days (one for each princess) and dances the princesses.