after u get to t he chest , get the item and run down to save, then u go back to climb the stairs from either side to exit to uk castle.
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actually after pressing enter to get chest ,press down and enter to exit the speech then u run down to save. second time going back after saving, u will appear in a strange screen like u stopped but actually u are in screen with sarah on top.go up for around 2 min u can see sarah but ignore her and go up to exit..
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Just today I picked up that yux shield from the chest simply walking into that chest, opening it and then press enter again, chest disappears and you can continue. Just don't release forward arrow the whole time and you'll be fine. Letting you go down after message without tossing you to endless stair is probably a bug
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Actually, when you reach the chest,
you open it, then when the message is on
screen you start holding the down button.
Then, keep holding while going through the messgae,
then when you get to the bottom you can save.