Atlantis. The Olympus Cycle, #8

He built it for love. Poseidon chose the rocky island in the outer ocean because of Cleito, a farmer's daughter on its central mountain who looked at a god and asked him not for magnificence but for enough. He gave her magnificence anyway. The ring-canals. The golden temple. The twin springs, one hot and one cold. The most extraordinary island the world had ever seen, built by a sea-god's hands from the material of the ocean floor, given to a woman who had asked for something smaller.
ATLANTIS follows the full arc: from the love that made it to the dynasty that inherited it, from the early generations whose divine blood kept them just and great to the later generations in which the divine thinned and the human hunger took its place. It follows the campaigns that reached toward Greece and the counsel of Zeus and the night the ocean reclaimed what the ocean made. And it follows Poseidon himself, moving through the Atlantic afterward, finding the ring-structures still visible in the submarine dark, touching the springs that still run cold and hot on the seamount floor.
Not a story of punishment. A story of what happens when a gift is mistaken for an entitlement, when the extraordinary forgets what it was built on - and what the sea remembers long after everything it loved has gone under. He built the most beautiful place in the world for a woman who asked only for enough. Poseidon and Cleito. The ring-canals, the golden temple, the twin springs on the mountain that had always been hers.
For generations the people of Atlantis were what their making intended: just, great, sufficient to their extraordinary inheritance. Then the divine blood thinned. The hunger took its place. And the sea, which had given the island, took it back. ATLANTIS tells the full story - from love to loss, from the first ring-canal to the night the ocean remembered it was the owner - and follows Poseidon into the long Atlantic dark where the ruins still hold the shape of what was given, and what was wasted, and what cannot be entirely lost.