Sky castles float along the Brink in Sambria from the Western Cloudwall to the Eastern Cloudwall. They may house semblances. Some semblances protect the castles while others have different purposes. Many castles may house treasures, dangers, or nothing. The Sky Raiders and other salvaging opertions, such as the Airmen and the Cloud Skimmers, raid Sky Castles for the treasures and items hidden there.
Sky castles are formed in the Western Cloudwall. They represent the peoples dreams which never come true. The castles enter the Eastern Cloudwall to be destroyed, semblances, treasures and all. Dandalus created the sky castles as a place where anyone's power who is fighting Ramarro is the strongest.
When Cole joins the Sky Raiders as a slave, he becomes a scout. He raids the sky castles to bring the items to the Sky Raiders. Cole's first sky castle featured a giant scorpipede with dozens of female semblances caring for it.
For Trillian's third challenge, Jace, Cole, and Mira appear on a Sky Castle to find Honor. The castle was one from one of Jace's many scouting missions. It featured a maze with horses in the center. The castle also featured a deadly creature that would hunt down any who set foot in the castle.
Cole, Jace and Violet travelled to Skyport for Cole's replacement Jumping Sword. Adam Jones mentioned a sky castle talking about a great treasure and the Torivor Ramarro. The trio came to the sky castle, and got past the defenses with Cole's Raw Shaping abilities. Here, a stone statue of Dandalus gave Cole information about Ramarro and the Void.