He mounted on the black horse, and away they went.

He reached the mountains, and he leaped the horse at the fire mountain
and was on the top. From the mountain of fire he leaped to the
mountain of ice, and from the mountain of ice to the mountain of snow.
He put the mountains past him, and by morning he was in Realm
Underwaves.

"You are come," said the prince.

"I am," said he.

"That's true," said Prince Underwaves. "A king's son are you, but a
son of success am I. We shall have no more mistakes and delays, but a
wedding this time."

"Go easy," said the Princess of the Greeks. "Your wedding is not so
near as you think yet. Till you make a castle, I won't marry you. Not
to your father's castle nor to your mother's will I go to dwell; but
make me a castle for which your father's castle will not make washing
water."

"You rider of the black horse, make that," said Prince Underwaves,
"before the morrow's sun rises."

The lad went out to the horse and leaned his elbow on his neck and
sighed, thinking that this castle never could be made for ever.

"There never came a turn in my road yet that is easier for me to pass
than this," said the black horse.

The lad gave a glance from him and saw all that were there, and ever
so many wrights and stone masons at work, and the castle was ready
before the sun rose.

He shouted at the Prince Underwaves, and he saw the castle. He tried
to pluck out his eye, thinking that it was a false sight.

"Son of King Underwaves," said the rider of the black horse, "don't
think that you have a false sight; this is a true sight."

"That's true," said the prince. "You are a son of success, but I am a
son of success, too. There will be no more mistakes and delays, but a
wedding now."

"No," said she. "The time is come. Should we not go to look at the
castle? There's time enough to get married before the night comes."

They went to the castle and the castle was without a fault.

"I see one," said the prince. "One want at least to be made good. A
well must be made inside, so that water may not be far to fetch when
there is a feast or a wedding in the castle."

"That won't be long undone," said the rider of the black horse.

The well was made, and it was seven fathoms deep and two or three
fathoms wide, and they looked at the well on the way to the wedding.

"It is all very good," said she, "but for one little fault yonder."

"Where is it?" said Prince Underwaves.

"There," sa