Follow the directions in these pictures:
http://bulbapedia.bulbagarden.net/wiki/Turnback_Cave
it worked for me in the diamond and pearl games and even in platinum.
Good Luck ;)
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The most valuable thing for you in this moment, a map of the cave: http://www.gamefaqs.com/portable/ds/file/925602/45230 Syaoran from Portugal ;D Go to: http://bulbapedia.bulbagarden.net/wiki/Wayward_Cave I have just used it to get back out of Wayward cave and am now using it to get Earthquake in the secret entrance
You Can Find Him The Fire Map Or The Cave Map Hope That Helped You
There is a map of Mt. Coronet in the Sinnoh region.
same as diamond/pearl
use the diamond etc from down the bottom and just6 drag it to where you want it.