Whats under the floor???

So apparently there is a hollow patch of floor beneath the carpet in the kitchen, slightly raised with a clear rectangular border . Seems to be a door to a cellar maybe as it is an old business building converted to a flat so a cellar would make some kind of sense.

I'm wondering why the landlord covered it up if it is a cellar as he could have put that to amazing use. Could it be he had stored his poor murder victims under there or could it be his and his wifes sex dungeon???? Could it be his secret stash of gold and silver treasure???

Who knows. Unfortunately can't find out. buggering hell!!!!!