"The first several layers of the skin are like a castle wall protecting the athlete from outside marauders, " Adams says.

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Local legend has it that Mary Queen of Scots spent a night there while a prisoner at Sheffield Castle, and in the perimeter wall there is a monument to a young man killed by a stag in the late 1400s.

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The king and his retinue had just returned and they too, along with the flies on the wall and everything else in the castle, fell asleep.

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Near the top, a path broke off and led to a flat open plot, where the castle should have been, but, save for an old stone wall, there were no ruins to be seen.

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"We now have a climbing wall and a bouldering wall next to the swimming pool, with a cafe and terrace overlooking Harlech Castle, " he said.

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