I never realized Lenna was a Playboy centerfold until years after I first encountered it, which was part of an MP in the data structures class all CS undergrads take at UIUC.
I had a similar experience. /r/turning had no memespam and good wood turning content, but I found the actual American Association of Woodturners forum to have very wide breadth and high quality information.
There’s also the foreman for video: https://youtube.com/watch?v=0cdM-7_xUXM