We did get little glimpses through Heartless, especially as we followed Felix's adventures and his recovery in the Haven. The Haven rests in the Between, neither in the Far World of Faerie nor in the Near . . . an uncomfortable place for mortals to dwell, despite the hospitality of Dame Imraldera! But for the most part, the Wood and the Faerie Realm remain a mystery.
But in Moonblood, Lionheart makes the plunge over his head into adventures galore, and we learn a little more about the fey world and the gates between the mortal realm and that of the immortals.
And, at the direction of Torkom the goblin, Lionheart sees his first Faerie gate:
"That is your Path, between those trees," Torkom said. "They are one of the Crossings into the Far World. You'd never think it to look at them, would you?"
Lionheart blinked. He could not remember seeing the two white birches before now. They gleamed strangely in the dark Midnight, ghostly and skeletal, and he wondered if the Wood had rearranged itself as it wished. (Moonblood, p. 143)
Lionheart passes through the two white trees however. And Goldstone Wood vanishes . . .
He felt no change around him, no strange sensation of distance, nothing he might have expected (though, in truth, he didn't know what to expect) from traveling across worlds. One moment, he was in the Wood Between. The next moment . . .
He stood in a forest of absolute emerald, so vivid, so vibrant, that it hummed the tune of its own color . . . (p. 150)
I couldn't possibly tell you all the adventures that befell him in that new strange realm, however! You must read it for yourself.
There are other gates to other realms as well, some gates that manifest different for various characters. The rules of the Faerie World are strange and varied, hardly comprehensible to mortal minds, after all! King Vahe of Arpiar, for instance, passes through a door way at the ruined tower of Carrun Corgar, and steps into the Netherworld of the Death-in-Life himself, which manifests as a wide, empty desert. When traveling to Rudiobus, Lionheart follows Bard Eanrin and Sir Oeric to a gate that looks like nothing more than a moss-eaten stump!
And some gates cannot be trusted. Take for instance the only known gate into Arpiar of the goblins:
"You know as well as I, old girl," says Eanrin to Dame Imraldera, "no one can enter Arpiar unless called from within. It doesn't matter what the bridge used to be. If Vahe does not want uninvited guests, he won't have them. You can cross and recross that bridge all you like and end up in plenty of unpleasant locales of our beautiful Faerie. But you'll not see Arpiar." (p. 264)
There must be hundreds upon hundreds upon thousands of gates in the great, sprawling Wood Between the Worlds! And we have only had a glimpse through a few of them. What other wonders, marvels, and terrors, might lie beyond the thin film that we know as Reality?