Oh man, MUDs were magical. I annoyed my parent to no end by tying up the phone line. Most of my best friends today are people I met on the MUD in the 90s, and we still keep in touch every day. It was amazing to be logging in and basically be living another life in a vibrant world.

I frequented one called Realms of Despair, unfortunately it's only got a few tens of people logged on at any time now.