Solution Sleuth Achievement in Stacking
Found all of the solutions to all of the Royal Train Station challenges.
How to unlock Solution Sleuth
Challenges are really easy in this game, especially with the hint system. Hint 3 tells you everything you need to know. There is no achievement for using no hints so you might as well abuse this feature if you're not sure how to complete a challenge or can't figure out any other solution. Hints refresh each time you complete a challenge, so when you use a hint again, it'll be telling you how to do the challenge with a different solution.
To use hints press at the Challenges section when you highlight the challenge you want to do. You'll have to wait several seconds between using hints.