Here is the full list of all 32 Castle achievements.
Buy everything from the shop (max. upgrades + max. items)
Prevent 20 bomb explosions
Roast 20 Poulthieves
Send 25 Silver Reds to the land of dreams
Fix 25 Clorm damage
Extinguish 20 castle fires
Complete Level 12 in Normal Mode
Fix 10 Clorm damage
Send 10 Silver Reds to the land of dreams
Complete Level 6 in Normal Mode
Fix 100 Clorm damage
Roast 50 Poulthieves
Roast 200 Poulthieves
Send 100 Silver Reds to the land of dreams
Put 20 Golden Blues to sleep
Put 50 Golden Blues to sleep
Put 200 Golden Blues to sleep
Extinguish 50 castle fires
Extinguish 200 castle fires
Get rid of 20 Burrholes
Get rid of 50 Burrholes
Get rid of 200 Burrholes
Prevent 50 bomb explosions
Prevent 200 bomb explosions
Earn a grand total of 50,000$ throughout a game (Money spent in the shop isn't deducted from this)
Make 100,000 points in the Protect the Castle mode
Complete the Protect the Castle mode
Complete the game in Normal mode
Fail 10 times
Acquire all the trophies of the Wall of Fame.
Complete the King Mode
Complete the Humble Builder mode