Ask HN: Are there any good discussion forums left?

When most people think of a forum, they probably think of Reddit. But Reddit is a news aggregation site, not a discussion forum. It is constantly pushing new content, old content is not meant to be consumed, and it is also not meant for meaningful discussion. This is reflected in the awful search feature, upvotes, etc.

A kind of site that was probably well known to most in the early 2000s and later was the forum. Threads could go on for years, and responses could be incredibly in depth.

Are there any active sites like that today?