This book truly sets a high bar for the subsequent books to follow. As it turns out, a lot of the "fiction" books in our world are actually true. All the lands we've read about exist as islands in the Archipelago of Dreams, and there is only one book of maps, the Imaginarium Geographica, which shows all the lands in it.
Unfortunately, to understand all of this book you have to have read through a good deal of books to understand this, including some works by Homer, Egyptian Mythology, and several books by Lloyd Alexander. There are far more, but unfortunately I don't have it in front of me right now so I can't list them here.