Aside from a variety of MUDs (see topmudsites.com for a bunch), one of my favorite Telnet destinations is HORIZONS (https://ssd.jpl.nasa.gov/horizons.cgi https:

Aside from a variety of MUDs (see topmudsites.com for a bunch), one of my favorite Telnet destinations is HORIZONS (https://ssd.jpl.nasa.gov/horizons.cgi https://ssd.jpl.nasa.gov/horizons.cgi). > This tool provides a web-based limited interface to JPL's HORIZONS system which can be used to generate ephemerides for solar-system bodies. Full access to HORIZONS features is available via the primary telnet interface.