Then there are the MUCKs, which tend more to social interaction and less pillage and plunder. Nose around the rec.games.mud.
Clients are a much better way to go MUDding than plain old telnet.
But if you're just curious, and have Netscape 2.0 or higher, you can connect through the MUD Connector web pages below, or any web browser if you have a telnet helper app configured. Mud Resources - look for client software and other goodies.