Castle

is a location in the game.

It can be accessed after you use the Bandit to pull the lever at the gate.

What to do here
You can meet the King and the Princess here. You will hear about a Basilisk descended upon the Castle, and threaten the King to give the Princess to it. You can decide to kill the Basilisk, or take the Princess and give her to the Basilisk.
 * Coin Bag: If you give the King Diamond, he will reward you will a Coin Bag. Unlocks the "King's Jewel" achievement.
 * Kill the Basilisk: If you give the King the Basilisk's head, the Bandit will become King, and marry the Princess. Unlock the "Long Live The King" or "The King Is Naked" achievement.
 * "The King Is Naked" achievement requires the Bandit to take a bath at the Pond before killing the Basilisk.
 * If you revisit the Castle after the Bandit became King, you will see him on the throne with the Princess besides. Unlock "New Order" achivement.
 * Take the Princess hostage: If you choose to give the Princess to the Basilisk, the Basilisk will reward you with a Treasure Chest. Unlock the "Treasure Chest" achievement.

After you give the King the Basilisk's head, or give the Princess to the Basilisk, the story of the Bandit will be completed, and the Kingfisher will appear.