Here is the full list of all 18 Idle Sand Castle achievements.
Earn 50,000,000 coins
Complete the construction of your largest sand castle
Reach the depth of the mine 100 meters
Dig 50 megatons of sand
Wake up 1,000 miners
Reach the depth of the mine 50 meters
Dig 500 tons of sand
Catch 1000 criminals
Catch 500 criminals
Earn 500,000 coins
Wake up 500 miners
Complete the construction of your second sand castle
Catch 100 criminals
Reach a mine depth of 10 meters
Wake up 100 miners
Earn 5,000 coins
Dig 5 tons of sand
Complete the construction of your first sand castle