you can only access turnback cave after you have the national dex, and once you have it:
1) go to veilstone city and go down to route 214
2) keep travelling down route 214 and stay to the right side of the route until you see a
route branching off.
3) go into the route branching off( it should be called spring path)
4) keep going down the spring path until you see something like a p***age way (entrance)
5) search the top side of the area and when you find a rock climbing place, go up it.
6) do not use the bridge, it leads to the middle of the lake and you can't go down it, you
can just go back to start of the bridge
7)go left, up and right until you reach the other side of the lake where there will be a
rick climbing place, and use it.
8) there should be an entrance to a cave, which is turnback cave, and you're there.
p.s, turnback cave is foggy so you will need defog.
turnback cave is full of lvl 45-60 (i think, rough guess) with pokemon like haunter,
bronzong and others(can't remember) so have pokemon lvl 60-70.
on every wall of every room, there will be a door which will lead to another room.
if you try to go back to a room, you have a very small chance of getting to the previous
room, because in turnback cave, dimensions are apparently distorted.
MAKE SURE YOU SAVE THE GAME BEFORE YOU BATTLE GIRATINA OR YOU WILL BE IN SOME TROUBLE!
by the way, after you caught or killed giratina, there will be a rare bone that takes it's
place when you come into that room again and when you take it, there will be another one
the next time you come back in that room, and again and again and again and so on.
also, there is a new pokemon game coming out called pokemon platinum on DS.
it's like diamond and pearl, but better.
go on this site for more info:
http://serebii.net/platinum/
