We moved into a new house about 8 months ago and we're trying to figure out all of our pool mysteries. At the shallow end we have this:
It appears to be some kind of swim jet to swim against the current. That's what it appears to be but there must be something missing. The two pipes stubbed up through the top of the deck have caps on them (I ground them off to try to figure out what's going on here). Those two pipes just go straight down to the "jets" that are below the water line on the wall. What is weird too is those two jets are connected inside of the pool wall. If I squirt water from the hose into one of the jets I can feel it coming out of the other one. The two "grates" in the bottom of the wall seem to be attached to each other as well. Here are some other pictures:
Inside one of the jets. You can see the pipe going up to the one stubbed through the deck. The pipe going back just loops around to the other jet.