Hard pipe formed before dug and put in ground. Gotta drive that steak and try it before I dog the trench.
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That looks like a fairly high spec pool, and my guess is they are dual main drains. Some people don't put them in and pools run fine without them. Two are put in to reduce the suction on a single opening, because that can be hazardous. Main drains can get plugged up or crack, and when that happens people often abandon them because of the cost of repair.
To find out, there's 3 valves on the intake lines to your pump. One may be marked 'drain' and if not, you could gently turn the valve to feel/hear whether there is flow or not. (wouldn't flow if it's plugged, might draw air if it's cracked, might not). If it's flowing fine, you could pull more water from the drain by throttling the skimmer valve, dive down and you should feel the suction around the edges. The covers are safety covers so a swimmer can't get their arm caught on them, or any other body part.
If the three valves are marked as something else (e.g. skimmer 1, skimmer 2, Vac) there's a remote possibility they're plumbed back to a skimmer, but based on other things you've mentioned I don't think so.
Just food for thought, no way to know until you test, and I hope it's helpful. Be careful messing with the valve at first - go slow, slight turns. There's a chance the drain line underground is clogged with gunk from the year's of no pool use. If it was, you might loosen the gunk and suck it up to the pump basket and need to manage that.
Gotta say, you've come a long way very fast!!