Telnet was the internet for me in the early years.

There was a bug at the local university dialup for students and teachers - if you failed to login three times it would drop you to a screen where it told you to disconnect but you could actually telnet from that screen.

I used that to go to a few internet BBS's, and then eventually to MUDs which were early text based multiuser RPGs.

sdf.org is another one that's fun to poke around on for nostalgia or learning.