Here is the full list of all 22 Cartonfall: Fortress - there are Defend Cardboard Castle achievements.
Win standard game on easy difficulty
Buy a crafting recipe
Win standard game on spring map
Spend some time in endless mode
Craft a weapon
Buy a new map
Craft 100 weapons
Win standard game on medium difficulty
Win standard game on hard difficulty
Destroy an enemy unit
Destroy 100 enemy units
Destroy 1000 enemy units
Destroy 50 flying units
Destroy 500 flying units
Win standard game without flag damage
Unlock all weapons
Unlock all 4 maps
Win standard game on summer map
Win standard game on fall map
Win standard game on winter map
Destroy large enemy unit
Set 50 traps