The Truth Is a Cave in the Black Mountains: A Tale of Travel and Darkness with Pictures of All Kinds, written by Neil Gaiman with illustrations by Eddie Campbell, is a lovely edition of the story first published in the Stories anthology. As such, I read it before.
Two men, one small and one large, walk through Scotland towards the Black Mountains on the Misty Isle (which is also called the Winged Isle), to find a cave. A cave where gold is to be found, or so men say. They find the cave. And, perhaps, also truth.
Neil Gaiman — The Truth Is a Cave in the Black Mountains (illustrated by Eddie Campbell)