Two Troll Hats In times gone by, a mountain king named Grim lived in a castle on a mountain. He was ugly and crafty, and robbed people of whatever fell in his way. For this purpose he had two hats. When he put on his flat hat, both he and his companions became invisible; and the other hat, an oven pipe hat, let the wearer see things that otherwise were invisible. In those days a farmer of Grimland prepared a wedding for his daughter, invited guests from near and far to the festivities. But he did not invite the mountain king. The king did not seem to be offended at this, but, on the wedding day he put on his flat hat and came to the wedding with all his people, and nobody saw them. When the wedding guests sat themselves at table everything that was brought in vanished, both food and drink and they could not understand where it disappeared. But a young peasant suspected the trolls were responsible, and rode straight away to the mountain. On the steps stood the mountain queen, beautiful and fine. She was alone there. Now she asked the rider how things were going at the wedding feast in Grimland. "The food is salt and the oil is sour," he answered. "That stingy farmer has hidden the wine and meat in the cellar where no one can find it. Now, if you give me the tall hat, he could find the hiding-place." Without mistrust the queen gave him the enchanted hat, and the young peasant hurried back to the festivities. Entering the hall, he put on the hat and saw at once the mountain king and his followers sitting among the guests, taking everything as fast as brought in. The peasant drew his sword, and commanded the others to do likewise. "Stab as I stab and cut as I cut," he cried, and began to slash around the table. The other guests followed his example and slew the mountain king and all his followers. From that time, no one has lived in the castle on the mountain but the queen.
Swedish folktale Source: http://oaks.nvg.org/stal13-15.html#hats