Please Help!!! in Marten´s Bluff, I can´t go into the eastern side of the castle because the door is walled How is it possible. I can climb the catapult but the door where the idol is, is closed because i cant´t put the switch who is in the eastern side of the castle

You have to go through:
SWAP -> MINE TUNNELS -> LOWER MARTEN'S BLUFF

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What he said was.. Enter swamp.. don't enter marten's bluff, go to the mine tunnels, at the very top of the mountain in that area, is a cartwheel. You can ride it to different locations, getting "stuff".. or you could ride it all the way to lower marten's bluff, allowing access where access was once denied.. in that area, you can enter an "indoor" secion of 'upper' marten's bluff.. in that area, after you've crossed the dart-firing column-room, is a switch which will open the door in upper marten's bluff where you'll get the idol.

Hey, thank you all for the help.
This forum is really the best.