Ghost Stone. (7th Gym)
If you didn't know about it.
On the third stage of the 7th Gym after you defeat the battle girl. There is a section right before the Gym-Leader that you need to solve in order to reach him. There is a stone on the first part after the battle girl. If you look there are 3 stones stacked atop each other in a line near the wall where the battle girl is. Walk towards the middle stone and pass through it in order to skip the last guy before the Leader.
Hope this helps.
Happy Hunting!!
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