Welsh national park (9)
I believe the answer is:
snowdonia
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">welsh national park</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for snowdonia that I've seen before include "massif region" , "Britain's third national park, designated 1951" , "National park in Wales" , "part of principality" , "peaks" .)