Before it was demolished, had the chance to swim in the Moskva pool: https://en.m.wikipedia.org/wiki/Moskva_Pool https://en.m.wikipedia.org/wiki/Moskva_Pool At

Before it was demolished, had the chance to swim in the Moskva pool: https://en.m.wikipedia.org/wiki/Moskva_Pool https://en.m.wikipedia.org/wiki/Moskva_Pool At 6,7m gallons (25k cubic meters) volume it was a bit larger and freshwater. The big deal about it was that it was used year round in Moscow. It was quite the experience to swim in it in the winter at -15C. -20C was the official operating limit.