Prism - that is a glass door to the small deck, so you are seeing into the yard.
It's the cat - (only non - Singer or Singer related item) every time one of them gets up there I start thinking of that Sesame Street song.
The cat gets up there through the hole at the top. We have a wood stove in that room and that opening goes into the stairwell a few feet above the landing. It does a great job getting the excess heat at the ceiling upstairs where it can be used. And the cats love sitting up there when we have a fire going as the convection currents keep that spot toasty. Trust a cat to find the warmest place in the house.
Here is a picture of cats in the opening taken from the other side. Though you can't see the floor, the outlet showing is at standard height, so the floor is just out of the picture.
And from the other side -
