Phantastes: To the Fairy Palace Puzzle

"I went on my silent path beneath a round silvery moon. And a pale moon looked up from the floor of the great blue cave that lay in the abysmal silence beneath. Gigantic forest trees were about me; through which, like a silver snake, twisted and twined the great river. The sleeping woods, in undefined massiveness; the water that flowed in its sleep; and, above all, the enchantress moon, which had cast them all, with her pale eye, into the charmed slumber, sank into my soul, and I felt as if I had died in a dream, and should never more awake. The stream bore my little boat with a gentle sweep round a bend of the river; and lo! on a broad lawn, which rose from the water’s edge with a long green slope to a clear elevation from which the trees receded on all sides, stood a stately palace glimmering ghostly in the moonshine: it seemed to be built throughout of the whitest marble." - Phantastes, by George MacDonald