What are some of your favorite communities that feature topics like literature, science, ecology, aerospace, technology, politics, history, arts, culture, theory, and debate?

Where do responsible, respectful adults go for discussions and for substantive, high quality posts and comments by decent human beings?

(Not just limited to academic/intellectual topics, could be anything from hobbies to defense contracts to careers to skills. Just looking for respectful, reasonably intelligent, informed, relatively engaged communities.)

Also, are forum aggregators like Lemmy and Reddit even the best places to find such communities outside of listservers, universities, and academic conferences?