New pool owner, old pool. I’m afraid to open it without knowing what it is.
It says “Charlotte” on it, must be the brand.
You can see my skimmer hole at the bottom of the picture… and why is there water on it? Could be the rain I guess. 
What it is for…I don’t know. It looks like a PVC pipe clean-out plug. Charlotte is a PVC brand. It’s hard to tell size, but it looks like a 3 or 4 inch clean-out. All my piping is 1-1/2" so that is rather large.
Obviously water leaking in from above. That shouldn’t be a worry.
Anyone else have this at your pool or have any thoughts?
Thank you for your reply!
They went all out to make this look exactly like a skimmer hole, same cover style and everything. So it must be important. The pool light is in that area under the water. Being square, you can obviously open it with the “square wrench” thing, and opening it would answer what it is for… but I don’t want to open it without knowing what it is because what if it’s something like a static water pressure plug (instead of a valve) or who knows. I hope someone can recognize it by sight and know what it is.
Is that pipe 4, 6, or 8"? Maybe it is a “shaft” to be able to pump water out from under the pool so as to be able to drain the pool and not worry about hydrostatic pressure lifting the pool
Or possibly a sewer cleanout for the pool pump or pool house?