The Star Wars Expanded Universe
The planet Wayland was discovered during the second expansion period of the Old Republic. A colony ship was filled to capacity and launched, but the world was logged improperly. Because of a simple error made by a careless, overworked clerk, Wayland cease d to exist in the logs and astrogation charts. The colonists did not know it at the time, but they were stranded. No supply ships would follow them, and no traders would be adding the planet to their routes. They had been cut off before they even reached their new home, and it was all due to a clerical mistake.
The colony ship full of humans ran into trouble during the approach to the planet and crash landed. Luckily, the scouting reports were accurate - Wayland had a pleasant, life-sustaining environment. It also had two intelligent indigenous species, the Myne yrsh and Psadan, although neither had advanced in technology past the bow and arrow stage.
For a time, the humans were able to rule. They had the repulsors, the powered weapons, the armour. But over time, equipment wore out and finally broke. The humans were forced to take up the technological level of the natives.
Centuries later, when the planet was rediscovered by the Empire, Emperor Palpatine paid a personal visit to the world. He liked what he found. He ordered all records of the planet's discovery stricken from the permanent logs. Then he had a personal storehouse built. Imperial engineers hollowed out Mount Tantiss, one of the highest peaks on the planet, and set up a maze of internal defensive systems. The actual placement of treasures was handled by Stormtroopers and members of the Imperial court. The Emperor would return occasionally to add things to his vault.
After The Emperor's death at the battle of Endor, Wayland was Lost again. The location known only to a few, most of who were now dead. Years Later Grand Admiral Thrawn found the location of Wayland. While looking for the Spaarti cloning cylinders left behind by Emperor Palpatine, he came across the dark side Jedi clone, Joruus C'Baoth. Thrawn promised C'Baoth Jedi students for him to train in the Dark Jedi, in agreement that C'Baoth would help Thrawn take control of the Empire. It was an uneasy truce at best, for C'Baoth wanted control over the Empire himself. The only protection Thrawn had from C'Baoth, was a tiny force-repelling animal called an Ysalamiri. Thrawn picked them up on the planet, Myrkr, and they could throw a force empty bubble over a ten meter wide area.
Thrawn Found the Spaarti cloning cylinders and began Cloning thousands of troops and operatives to defeat the New Republic. After hearing of the intensified cloning that Thrawn is doing, Mara Jade decided to make her peace with the Rebel Alliance and aid them in finding Wayland. Together with Luke Skywalker, Han Solo, Chewbacca and Lando Calrissian, they travel to Wayland to destroy the cloning facility. However, using tissue from the hand Luke had lost on Bespin, Joruus had grown a clone of his own. Luke faced his clone, Luuke, in the throne room of the Emperor's Mount Tantiss facility. When Mara Jade killed Luuke, Luke joined with her and Princess Leia to defeat and destroy C'Baoth.
Most Information from the Thrawn Trilogy books written by Timothy Zahn
Heir to the Empire
Dark Force Rising
The Last Command