Underground room (6)
I believe the answer is:
cellar
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">underground room</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for cellar that I've seen before include "Room below ground for storage" , "Store for wine, possibly" , "Wine-store" , "Room where wine is usually stored" , "Wine vault" .)