Is this a drain cover or an electrical outlet cover?
My bet would be on it being a receptacle. Typically floor boxes like this are installed raised up a little, so as to accommodate carpet or other flooring.



I would also bet on it being a single outlet. Most likely the center cap is covering the outlet and the outer screws are there to hold everything on. Since we can see a shadow from the center box, I'd say pry it off of there as best you can.