Here is the full list of all 18 King's Heir: Rise to the Throne achievements. It takes around 2-3 hours to unlock all of the achievements on Windows.
Find all the Collectibles in the Bonus Chapter.
Place the crown on Randall's head.
Finish all the Hidden Object Puzzles without using Hint.
Take a moment for a tankard of liquor.
Feed the animals, big and small.
Take a leap of faith into the water.
Find half of all Collectibles in the Main Story.
Finish 3 Hidden Object Puzzles without using Hint.
Finish the Lock Picking Minigame without using Skip.
Finish a Hidden Object Puzzle with less than 3 mistakes.
Finish the first Fight Minigame without using Skip.
Find the first Collectible.
Finish a Fight Minigame without making a mistake.
Finish the final Fight Minigame without using Skip.
Find all the Collectibles in the Main Story.
Finish a Hidden Object Puzzle in less than 20 seconds.
Finish a Minigame in less than 30 seconds.
Pet all the animals, even if they run away.