No, I ma quite positive about that because I have tried going inside it straight after the main event and nothing happened at there.
Theres a map? Really? Thanks! I wouldn't mind a link if i cant find it, and also, i already finished the game, but i got Giratina instead, which is why im kinda askin where the green diamond is, but a map of the Shadow Valley? Sweet! *Goes to find the 18 sprouts, never to be seen again... 'Till tommorow..)