Written by Graham Nelson. One of the first major games programmed in the Inform 7 language. The source code is freely available and extensively annotated.
"It used to be said that there are two kinds of magic-user: those who have been to Tolti-Aph, and charlatans. It used to be generally understood that the attempt to prove oneself in the unforgiving society of Tolti-Aph was a bid for rapid level advancement or else romantic, thin-young-mage-in-midnight-black-robes death. The closer you get to the wilderness island vaguely marked 'Tholtaff' on the agate globe in your great-great-grandfather's study, the better the alternative sounds: settling down in some coastal village, perhaps, a little weathermongering, some polymancy, and helping out with the nets after a bad storm. Retire at maybe level 3, with most of your experience points gained from observing rare fish-based poisons carry off those villagers careless about gutting. Publish an awesomely tedious monograph on the correct usage of the 'untangle rigging' spell. You know, the good life."