The attached pic is while the pool was empty (grubby fingers included for size perspective). This is in the pool wall, on the opposite side of the pool from the IG skimmer, about 12-16" below the deck. There's nothing in the deck immediately above where this is, though the leveler is about 2' away. I have no idea what it is.

Also, probably a dumb question, but while the pic is there... That pool wall is plaster, right? Is that a certain type of finish? I read somewhere that Shasta had some sort of "Shasta Sand" and quartz finishes... Not 100% positive what this is and/or if there's any special care required for it.

I don't recognize the fitting, but the surface appears to be some kind of quartz finish. Quartz pools are maintained the same as plaster pools, but will usually last longer.

Is it completely covered and full of water?

Almost looks like there is an eyeball in there that was covered/sealed up?

That's a Fiber Star light lens. Here's and example.

I assume you have Fiber Star lights.

It is covered (now) and yes, there appears to be water inside of the lens.

So it just clicked... There is some weird and old-looking tower thing about 8' away that says "FiberStars" and model FS3 on it. This is the ONLY lens in the pool... In fact, I always thought it was weird that there was no light in the pool, but apparently this is supposed to be it? When I turn on the tower, it has a fan in it and casts quite a bit of light onto that area of the pool deck, so never thought any more of it than that.

So now, I'm guessing that lens is NOT supposed to be full of water (it does not light up) and is probably shot. I'll poke around and see if I can figure out how to replace that. Hopefully it can be replaced underwater, since I literally drained and refilled the entire pool just days ago. :-/ If it's even half as cool as some of the Fiber Star pictures I just looked at, I'll be excited about this pool again.

Thank you for pointing me in the right direction!

I think the way those work is there is a large external light source (where you hear the fan) then light is carried to the lens via fiber optics. Thus, the water in the lens should not really hurt the light at the pool, since it's being created outside the pool.

Robbie is correct. The light source is the box and a bundle of fibers carry the light from the box to the wall fitting. Unfortunately the lens cannot be removed underwater. It just screws out by the way. I'd open the box and see what's going on. There should be a lamp, color wheel and then the fiber bundle.

Sure enough, it's a fiber light. Opened up the box above deck, and there is an ultra-bright light shining through a glass disk, and onto the fiber. On the glass disk and the end of the fiber, there was a TON of dirt/dust/grime caked on there - no wonder nothing was getting through. I carefully cleaned those up and put it all back together, and now there is light! I never would have guessed that "thing" was a pool light.

This old crummy model apparently does not have a color wheel, just a fixed glass disk (looks like it used to be red, but it's just faded nothingness now) and there's only the one lens in the pool. It only lights up about 1/3 of the pool because of the shape and where the lens is located. Pretty disappointing, but oh well, it'll do.

Thank you all for helping me figure this out. You guys are incredible!

Whenever you get the water level below that lens again remove it and clean it out and clean the ends of the fibers. You'll be surprised how bright it is once it's all clean. Replace the o-ring on the lens when you remove it.

If the glass disc is removable you could go to a glass shop and have a couple disks made to same size, specs and possibly different colors. If they can't do the different colors you could go to any glass craft store and get some glass paint. This would then allow you to have colored light without replacing the system.