Download the offline version of Wikipedia and some backups of GeoCities. The good old days are in the past and immutable, you can look at it, but you won't be able to meaningfully interact with an online society that no longer exists. Because of that, it will feel more like being in a museum than actually experiencing the old Internet.
That said, there are corners of the Internet that have changed little. Forums for special interests. I'm on a synthesizer/musician forum (MOD WIGGLER) and it is pretty old school. There's are guitar forums like TDPRI (Telecaster Discussion Page Reissue) that are also pretty much unchanged for decades. I used to post on NESdev forum, which is a hobby retro game programming forum. But I haven't touched it in a decade+