"I wonder if anyone here would know," Magnus says, thoughtfully, as he flings open another door.

He pinwheels for a moment, throwing an arm out to keep Galahad from stepping forward. The threshold is cut off, jagged, falling away in a sheer cliff face. Inside is an enormous chasm. Flickering ephemeral lights glint here and there, and either their sources are tiny or the chasm is the deepest one Magnus has ever seen, stretching infinitely in either direction. From deep below, there's a slithering sound of something rough scraping against rock.