Large cave (6)
I believe the answer is:
cavern
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">large cave</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 cavern that I've seen before include "Subterranean chamber" , "Large underground hollow" , "Large 24 chamber" , "vast enclosed space" , "Craven in a cave" .)