Underground prison cell (7)
I believe the answer is:
dungeon
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">underground prison cell</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 dungeon that I've seen before include "Keep" , "Uncongenial accommodation" , "prison the result" , "Dark place of confinement" , "old prison" .)