Welsh mountain region (9)
I believe the answer is:
snowdonia
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">welsh mountain region</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for snowdonia that I've seen before include "peaks" , "mountainous area" , "mountains" , "Mountainous Welsh region" , "Welsh national park" .)