Fitness center?
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">fitness center</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 gym that I've seen before include "Area for physical exercise in short" , "Place to get fit" , "Physical education" , "Briefly, a keep-fit place" , "Fitness centre" .)
(Other definitions for core that I've seen before include "Heart of the matter" , "Crux" , "Central or most important part of something" , "Kernel" , "The innermost part" .)