" The track led into a sort of tunnel made of forest. They left daylight behind, a thousand leaves hemming them into dusky shade. As she traipsed behind Jack's torn blue jacket, he squinted into the foliage, hearkening to every cracking twig or bird-chirrup. After what seemed an age, they came out into blessed sunshine again. They were in a clearing, their ears filled with a thundering wind, the air itself trembling. A few paces further they came upon the source: above them, a waterfall tumbled from a clifftop as high as a church steeple. The water fell in milky blue strands, shooting spray in the air that danced in rainbows of gold, pink and blue. At their feet was a deep and inviting lagoon. It fair took her breath away.
Jack crouched to look at the pool's edge, where a mud bank was scrabbled with marks.
"We should go back," he said. "Something drinks here."
She didn't care. She was spellbound. "Look, a cave!" Across the lagoon stood a dark entrance hung with pretty mosses, like a fairy grotto.
"Just one peep," she whispered, for there was something powerful and secret about the place. "Then we can go back."
But Jack was still peering at the tracks around the water's edge.
"Whatever drinks here, it's not here now. I dare you, Jack. A quick look around the cave and then we'll be on our way." She had a notion, from some story or other, that caves were places where treasure was hidden; she reckoned pirates might have left jewels and plunder behind long ago.
"It's the end of the rainbow," she laughed. "Let's find our crock of gold. "

― Martine Bailey , A Taste for Nightshade