Typical, isn't it - you have writer's block for ages and then a whole lot comes out at once.
Anyway, this here's my first ever Steven Universe story, so please bear with me. Hope you like!
The City on the Hill
Prologue
Despite what the explorers of Europe liked to tell themselves, there were very few places in the Pacific Ocean that were truly undiscovered by the turn of the eighteenth century. The Polynesians had seen to that - undertaking vast voyages across these unforgiving seas long before European ships had ventured into the Atlantic, never mind the Pacific. These seafarers often sailed and established great civilizations - in modern New Zealand, in Fiji, in Hawaii, and in countless others.
But never here.
Some had tried sailing to this island, but all had disappeared. It was an anomaly - a perfectly ordinary looking island, covered in green growth like many others, volcanic but dormant. It looked unremarkable, and yet nobody who came ever returned.
Attempts to settle the island were ramped up after the 1600s, when bold (some might say hubristic) Dutch mariners learned of the island and it's record and decided to make history as the first men to return from there. They failed, time and time again. Not only did the men vanish, so too did their ships and all of their stores. The same fate was met by French and British sailors in the eighteenth century.
Eventually, even the most pigheaded captains got the point. When Captain James Cook sailed by whilst captaining HMS Discovery, he drew some charts but pointedly declined to sail too close. He was the last European to visit for decades. The distractions of the French Revolutionary and Napoleonic Wars saw to that.
Then, in 1845, in a world that claimed to be ruled by reason and science, the Royal Navy decided to put 'old superstition' to rest. A steam frigate, HMS Reliable, was dispatched to the Pacific with orders to 'raise the flag and return post-haste with a report.'
The voyage was beset with problems from the very beginning. The commanding Commodore Forrest was an experienced officer, one of Lord Nelson's protégés, but he was elderly and gout-ridden. The first officer was his son, Lieutenant Benjamin Forrest, and while he was a competent officer he was resented by the other officers for what they saw as nepotism. The Captain of Marines was a drunkard who left the majority of his work to the sergeant. There was not enough fresh food, necessitating a trip around the dangerous waters of Cape Horn so that they could restock on the way. The sailing master died of dysentery just before they crossed Drake's Passage, making navigation that much more difficult.
The ship, despite its name, was very new, which meant she had a long catalogue of problems. She was driven by an underpowered steam engine that made little in the way of speed, and there were barely enough men to man the sails. The boiler had a very, very nasty tendency to catch fire without warning. The paddle-wheels jammed constantly. The weight of the ship was badly balanced, which made her a terror to sail in stormy weather - which was nearly constant in the voyage around South America.
By the time they reached the island, the crew was almost on the point of mutiny. Nearly every sailor refused to disembark the ship when they anchored, and some were muttering about making off for America.
The captain decided to take the marines (excluding their totally useless captain), Lieutenant Forrest and two of his less loyal officers ashore with him, leaving the second lieutenant in charge. The second lieutenant was popular and considered loyal, so it was hoped his presence would calm the crew.
There was never a chance that Forrest and his party would return to Great Britain. Not simply because of the island and it's apparent curse, but because the Reliable immediately raised anchor and sailed for America as soon as her captain was out of sight. The Reliable mutiny would lead to a brief diplomatic incident between Britain and America, a few exaggerated novelizations and the commissioning of the ship as the American USS Keystone, but otherwise would become a historical footnote. Forrest and his companions were presumed to have starved on the island and quietly forgotten about.
Commodore Forrest was not dead.
In fact, not a single person had ever died in the multitude of failed voyages to the island.
The island - or rather, the volcano whose peak formed the island - was created from the wreck of a Gem ship. It was a space liner, a ship which carried aristocratic gems in the very height of luxury to prospective colonies. On its final approach to Earth, it was hit by a freak comet and slammed into the Pacific Ocean - the crash and ensuing explosion formed the volcano.
Most of the Gems aboard were shattered in the landing, but a third of the ship's passengers and crew survived. With all communications with the outside lost, the ship's company decided simply to carry on with establishing a colony inside the newly-formed volcano. With the end of the Rebellion, this city became the last piece of Homeworld civilization on Earth.
They named it after the liner - Providence. And as time went on, Providence acquired new denizens - curious humans captured on the island...