On of the best "third place" locations I've had was a gym as well. This was about 15 years ago, before iPhones and Airpods, etc. existed, or were as prevalent, so it was easy and common for gym regulars to strike up conversations and get to know each other.

I don't go to the gym anymore, but a few years ago when I resumed for a bit, everyone was on their phone, or dead-eyed while listening to music or a podcast, etc, and not interested in talking to anyone.