The Garden of the Hesperides is Hera's garden in the west, where there is a single tree on which golden apples grow. It is guarded by Ladon, a hundred-headed dragon.
History
The apples were planted from the fruit branches that Gaea gave to her as a wedding gift when Hera accepted Zeus. The Hesperides were given the task of tending to the grove, but occasionally plucked from it themselves. Not trusting them, Hera also placed in the garden a never-sleeping, hundred-headed dragon named Ladon as an additional safeguard.
The golden apples were called the "Apples of Immortality", and it was believed that whoever ate of them will become immortal.
Hercules' 12th labor was to retrieve the Golden Apples from The Garden of the Hesperides. First, he flattered the Hesperides, but they didn't give him the apples. Then he found Atlas and convinced him to give him the sky for a little so Atlas went to see his daughters and they gave him a golden apple. Then Atlas gave the apple to Hercules.
Appearance
In The Titan's Curse, Percy described the Garden of the Hesperides as the most beautiful place he had ever seen.
The grass shimmered with silvery evening light, and the flowers were such brilliant colors they almost glowed in the dark. Stepping stones of polished black marble led round either side of a five-storey-tall apple tree, every bough glittering with golden apples of immortality.
Percy also stated that he could not describe the reason for the appeal of the apples, but as soon as he smelled their fragrance, he knew that a single bite from one of them would be the most delicious thing that he had ever tasted. In fact, if it were not for the dragon coiled around the tree, he wanted to step right up and pluck an apple.
In Percy Jackson's Greek Gods, Gaea's wedding gift to Hera was described as a "young apple tree bearing solid gold fruit".
Percy Jackson and the Olympians
The Lightning Thief
It does not appear, but it is said by Luke that he was scarred while attempting to pick apples from the tree by the dragon Ladon. He failed in his quest, but he managed to return with one of Ladon's claws.
The Titan's Curse
Zoë Nightshade, a former Hesperide, attempts to get past Ladon, and get her and her companions to safety, but Ladon realizes after a few minutes that Zoë is no longer a Hesperide and attacks her. She and her fellow quest members manage to escape, but Zoë is poisoned by Ladon.