Golden Palace Of The Immortals
From Madame Song:
The Golden Palace of the Immortals may or may not actually exist, but in stories, it is the place where the Twelve Immortals live when they are not in this world; to eat an entire golden-skinned peach from the Golden Palace of the Immortals is to become an Immortal. Occasionally, small slices of such a peach, or just nectar is granted to one to whom an Immortal wishes to show favor. There are stories of those who try to steal peaches - the only such story she knows of which ends anything close to happily is the one in which the Great Monkey Spirit himself attempted to steal one of the peaches to give to an enemy...
The context of this information was "Why would someone ask me to get a golden-skinned peach from the Palace of the Immortals?". The provisional answer is that it's somewhat like asking for the moon.