A World of Ice and Fire, the book Salon critic Laura Miller likened to the Silmarillion of George R.R. Martin’s fantasy world, is probably most notable to many fans for what it’s not: the long-awaited sixth installment of A Song of Ice and Fire, the fantasy series the new book is a companion to. It also doesn’t tell the reader much about what’s happening, or will happen, on Game of Thrones. But the book, the result of six years of collaboration between Martin, two superfans, and over two dozen artists, is a testament to the staggeringly detailed “secondary world” Martin has created — a world that even five books and 40 episodes of television couldn’t fully contain.

Moderated by Miller, last night’s event at the 92nd Street Y was an opportunity to explain A World of Ice and Fire and go through its highlights, one maximalist illustration at a time. Martin’s writing process, he explained, is in some ways the opposite of J.R.R. Tolkien’s. The Lord of the Rings author was a scholar and linguist, almost more interested in constructing the languages and history of Middle Earth than the stories he set in it. Martin begins with story and character, but like all modern fantasy authors, he works in Tolkien’s shadow; where fantasies were once simplistic narratives, today’s fans expect background, and lots of it. Still, if Middle Earth was an iceberg, with most of its substance lying below the surface of the original books, Westeros was initially “some ice on a raft.”

Over the years, however, Martin’s initial strategy of “[making] up a bunch of kings’ names and dates” for his indices ran into some problems. For one, Martin had developed a firmer idea of Westerosi history, history his characters would mention in passing and readers would ask about via fan mail. And there were some inconsistencies that fans picked up on — fans like The World of Ice and Fire co-authors Elio M. García, Jr. and Linda Antonsson. They developed a relationship with Martin, who still uses them to fact-check his own details.

When García and Antonsson signed on to help write a companion book in 2008, the initial plan was for the two of them to compile just 50,000 words’ worth of information already published in the books, with the bulk of the volume given over to illustrations. Of course, as with most Martin projects, there ended up being more words than expected (“I wrote like 300,000… at that point my editor’s head exploded,” Martin laughed; the audience applauded), but the visual emphasis remained. “I wanted it to be beautiful,” Martin explained, but The World of Ice and Fire afforded another opportunity: accuracy, or at least the ability to show readers what Westeros looks like in Martin’s imagination, unconstrained by the realities of shooting a television show.

At this point, Miller started pulling up the images, transitioning the conversation into full-on geek mode. The audience learned, for example, that the inside cover image of Dragonstone (Stannis Baratheon’s home base on Game of Thrones) shows the castle as Martin envisioned it: a monolithic, physically impossible mass of stone, with towers shaped like dragons, scaled walls, and not a brick in sight. And then there’s the Iron Throne, which is taller, uglier, and more terrifying than the now-iconic version from the TV show. Game of Thrones may use the biggest soundstage in Europe, but it’s still not big enough to hold the multistory, asymmetrical structure Martin wrote into existence: “To build this monstrosity would blow the budget of the entire episode. And it wouldn’t even fit on the set!”

Of course, Martin clarified, “This is the difference between books and television. I can say the Wall is 700 feet high, but I don’t actually have to build a 700 foot Wall.” Which is the appeal of both A Song of Ice and Fire and its companion book: the ability to invent a new world without the constraints of the actual world, both in words and, now, in images.

Miller posited that the book might appeal to those obsessed with the edges of maps; given that A World of Ice and Fire provides the history of every Targaryen king to ever rule and background on foreigners as obscure as the Rhoynar and the residents of Yi Ti, and clarifies inconsistencies like Game of Thrones‘ consistent lack of battle horses, that’s bound to be an accurate description. This is a book for detail hounds — longtime readers and viewers who, like me, will spend hours poring over the details of the Blackfyre Rebellion or the history of the Free Cities. It doesn’t have much bearing on the plot — Martin kept the book thoroughly spoiler-free — but it’s a look into the mythology that gives the books (and series) life. And for fans eagerly awaiting book six, it’s new material to make the wait a little shorter.