From "The Sins of Prince Saradine" by Chesterton

They had moored their boat one night under a bank veiled in high grasses and short pollarded trees. Sleep, after heavy sculling, had come to them early, and by a corresponding accident they awoke before it was light. To speak more strictly, they awoke before it was daylight; for a large lemon moon was only just setting in the forest of high grass above their heads, and the sky was of a vivid violet-blue, nocturnal but bright. Both men had simultaneously a reminiscence of childhood, of the elfin and adventurous time when tall weeds close over us like woods. Standing up thus against the large low moon, the daisies really seemed to be giant daisies, the dandelions to be giant dandelions. Somehow it reminded them of the dado of a nursery wall-paper. The drop of the river-bed sufficed to sink them under the roots of all shrubs and flowers and make them gaze upwards at the grass. "By Jove!" said Flambeau, "it's like being in fairyland."

Father Brown sat bolt upright in the boat and crossed himself. His movement was so abrupt that his friend asked him, with a mild stare, what was the matter.

"The people who wrote the mediaeval ballads," answered the priest, "knew more about fairies than you do. It isn't only nice things that happen in fairyland."

"Oh, bosh!" said Flambeau. "Only nice things could happen under such an innocent moon. I am for pushing on now and seeing what does really come. We may die and rot before we ever see again such a moon or such a mood."

"All right," said Father Brown. "I never said it was always wrong to enter fairyland. I only said it was always dangerous."