Ulmo was bored. And this was never a good thing.
The Lord of Waters was aimlessly strolling through the bottom of the endless ocean, playing with the waves that followed his every command. Ossë and Uinen were away on a date at the shores of Beleriand Ossë so liked to spend all his time at, helping the elves, and the Vala was left alone. Well, not alone, one could never be truly alone in the ocean, but Ulmo was bored, which was pretty much the same thing.
All around him, under the glistaring sand and into the darkest of caves in the most remorse places, dancing in the crystal-clear waters were all kinds of animals, floating around and keeping him company. Ulmo waved his right hand and played with the enormous body of water in which he was inside, making bubbles pop up, and watching them as they floated upwards, trying to break the surface and disappear in the sky.
Ulmo dwelt alone, no Ainur save his two faithful Maiar had gone with him, but he did not entirely mind. His realm of seemingly endless green and blue waters was filled with life, the life of the sea and he was content in it. He was content to spend his time with the creatures that lived inside it as he did, and sometimes he liked to blow his horns and make music, enchanting the sea with the sweetest of melodies. Ulmo rarely ever left his domain, only to attend the council of the other Valar and then only when very important matters had to be discussed. It had been a very long time since his presence had been required, and Ulmo was not the best at keeping the track of time.
A dolphin twirled happily around him, nudging him with his nose and Ulmo smiled, reaching out a hand to pet it. The dolphin squealed happily at the touch, and the fast and excited movements of his tail unsettled the sand below them. Ulmo watched the brown and yellowish granules rise and float among the clear waters. Then suddenly, an idea came to him and he moved his hand around, and the ocean moved with it, taking the golden granules with it and twirling them around with the movement of the waves.
The Vala thrust his hand upwards, grinning as he did so, until the golden granules of sand were everywhere around him like a cloud of fog. His eyes sparkled with a childish glee as he continued to play with the waves, making the sand float around.
It was hours later when Ossë and Uinen returned, that they found him sitting at the bottom of the ocean, playing with a tiny red crab in front of his newest creation.
"My lord," Ossë said, eyeing the huge construction in front of him, "what is this?"
"My dear Ossë, what do you think it is?" Ulmo smiled at the dumbfounded expression his Maia wore.
Behind him, standing proudly at the green and blue gleam of the crystal waters of the ocean was an enormous sand castle.