[Note: Links have been added.]
The game itself is a conglomerate of techniques and ideas from several gaming cultures and traditions. It has gone through many versions. It is possible it will always be in a state of flux and mutability, hard to pinpoint. However, one way to start is to try to remember the many sources of the design. These are in pretty random order!
Clyde Rhoer’s Silence Keeps Me A Victim (the game isn’t available anymore, I believe, but there’s an interview with the author here.) I have yet to play this evocative game; but I’ve used Rhoer’s dream technique as a central piece of the Dream scenes in Society of Dreamers.
My own Archipelago. The basic group attitudes of trust and responsibility and the focus on group processes is central.
Jonathan Walton’s Mwaantaangaand is probably where I first picked up the idea of having scenes represented physically on a board. I’ve later used it in different ways in other games; here it inspired the Ouija board mechanism.
Ritual ideas from Nordic larps such as those designed by Erlend Eidsem Hansen and Eirik Fatland.
Ole Peder Giæver and Martin Bull Gudmundsens Itras By – the prime game of European surrealist fantasy.
Ben Lehman’s Polaris was the first game I played which really deconstructed the GM role and distributed it among the players.
Willem Larsens blog College of Mythic Cartography.
The situationist international and their psychogeography.
The ideas of dream researcher Jim Ashtrottle.
I’ve discussed the game extensively at rollespill.net and in real life, and it’s hard to remember what suggestions I ended up incorporating. I know it was Anders Nygaard (designer of the New Middle Ages) who inspired me to let the players create/explore the mnemosite as part of play, and Ole Peder Giæver (designer of Itras By) who said the mnemosite could be undefined to begin with. And, of course, the basic idea was a challenge from Øivind Stengrundet (designer of Wanderer).
I’m sure there are many, many more. But this will give you an idea of what sort of concepts the game is built of.