Orthanc is an RPG on the PLATO network. It draws heavily from Pedit5 but has larger dungeons, more monsters, spells, etc. The player takes on the role of a knight with the goal of retiring as a proven warrior. The knight has various statistics (strength, intelligence, constitution and dexterity) which have an effect on the actions taken in the game. The game is shown in a top down perspective with statistics, experience, spells and inventory shown at the bottom half. To get experience points the player needs to exit the dungeon and convert the accumulated treasure. Levelling up gives access to more spell units (required to cast spells) and hit points.
The game features an automap (added in a later update, 25 years on) and the player can encounter other players in the dungeon and can chat or fight with each other.