The college where I work had one, it sat empty for years because it wasn’t part of a gym complex (we have those, too), but a pool that came with a random building that the school purchased. The pool hadn’t been used for years.
Recently it was turned into a lounge, it’s nice enough. There are cafe tables around the area that used to be the deck, and then wide tiers were built up on the slope of the interior of the pool, and there are clusters of chairs on each one. At what was the deepest end of the pool, there’s a flat area that can be used for presentations – the speakers are standing in the deep end, and the audience is seated up along the tiers, like an amphitheater.
Originally there had been some of that cool tilework decorating the pool area (I think it was art deco era) and I had been hopeful that some of that could be preserved and incorporated into the lounge, but apparently after many years of neglect there wasn’t hardly anything left by the time the space was converted.