The tarnkappe is the name of an alp's magic hat. In German it translates to "camoflage cap", and it can either describe a hat or a cloak that renders the wearer invisible at will. The idea of the tarnkappe may have originated from the epic poem "The Song of the Nibelungs", in which the king of Dwarves Alberich guards the treasures, a magic ring and the tarnkappe, a cloak of invisibility.
In alp lore, the Tarnkappe grants the wearer the power to change shape from mist to various animal forms. In all of the animal forms, the hat remains visible. An alp without its hat is nearly powerless, so he guards his hat closely and offers a great reward for the return of a missing tarnkappe. Stealing a tarnkappe is not as easy as it sounds though, so what reward an alp offers for the hat's safe return is unknown.