This is the master bathroom of a house I am working on. My clients didn't build the house -- we are remodeling the remodel of the previous homeowners that happened about 6 years ago...

What is this 3/4 trimmed hole stuck in the corner of the wall????? We can't figure this out!

Here, let me turn the light on and see if that helps you out.

It has a tiled floor, is about 15" deep and the light is all the way at the back. What the ????? 

It's become a really fun game for me as I take all of my subs to it and ask them for their opinion. It's a head scratcher, for sure. Please, one of you incredibly smarty readers, splain this to me.