Ilex Forest is located south of Johto and it will be found left/west of Azalea Town. Ilex Forest is protected by it's very own protector Celebi which is a legendary Pokemon. On some Pokemon games, Celebi will appear in the forest near the shine. In Pokemon Heartgold/Soulsilver, when you take the Celebi from a event to the shrine, it will activate a time travel event. Also, if you take the shiny Pichu to the shrine, you can get the spiky eared Pichu.