Note to self: Ellen likes large, muscular men with spiky hair and fishnet shirts. She is entirely unique in this regard, I'm certain.
The layout of this underground layer may be a bit confusing, but there's only a little of it that's particularly important. The big room where Cat--er, Elliot (I seriously typed "Cat" instead of Elliot without thinking) was being held is overlooked by the room where Grace, Damien, and the scientist are, and there's that walkway where Vlad is now.
So, let's see... Big room, seemingly one entrance on the ground level, another room to observe the big room from... This is clearly where Grace and her brothers used to play kickball for fun, and everyone wanted to watch!
Or maybe they did training exercises in there, and those columns Elliot were tied to could have things tied around them for the puroses of those exercises. Either/or.