I am so tempted to set up a, like, BSS-style Telnet server. (Did you know JPL's Horizons ephemeris database is accessible via Telnet? Pop open a terminal and enter telnet horizons.jpl.nasa.gov 6775!)
CSS crimes are wonderful -- but imagine the VT100 ANSI escape code crimes you can get up to!
Also, Telnet-based MUDs have made me feel "embodied" online more than any other social medium. Have you ever tried a MUD? TopMudSites (now read-only) has a good selection. I used to play Achaea obsessively!