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