for me it was this forum site called VocaloidOtaku back then around 2014 (I know it sounds cringey) when I was 13-14 yrs old and it was about, well, vocaloids and anime but mostly vocaloid and people who make music using vocaloid. It was a forum much like spacehey, I remember visiting the site everyday, posting and responding to comments and making new friends.
2018(?) comes and eventually they had to shut it down the site because it wasn't gaining traffic as much as it used to before. I already left the site long before it shut down (around 2017) but I still was sad when I heard of the news.
I still visit the site from time to time using wayback machine for nostalgia, I even see my old posts there and the userbars I made for fanclubs.