MUDs were my introduction to telnet- I grew up a university kid and had access to Wesleyan's minicomputer EAGLE.WESLEYAN.EDU running OpenVMS. I used it to telnet to CMU's TinyMUD and later other TinyMUDs around the country. I recall OpenVMS's telnet had a problem with newlines/carriage returns so all the text was staircased, so I ended up learning C and writing a MUD client. I still habitually use telnet today even if netcat and many other tools have replaced it.
All of that was foundational for my career and I still look back fondly on the technology of the time, which tended to be fairly "open" to exploration by curious-minded teenagers.
Ah, my grandfather was a ham (N4MDB) and he always tried to get me interested in it, but I had to tell him I preferred the internet (this was late 80's, so few people actually had internet). Later when I read Stevens networking books I learned there was a whole Hawaii-based packet radio (ALOHAnet) , and the UC campuses had intercampus microwave networking for a while as well. I actually still remember him telling me about bouncing radio waves off the atmosphere which seemed like magic to me at the time.
All of that was foundational for my career and I still look back fondly on the technology of the time, which tended to be fairly "open" to exploration by curious-minded teenagers.