Here is the full list of all 26 Hold The Door achievements.
One round on easy difficulty won!
One round on medium difficulty won!
One round on hard difficulty won
Stopped 100 monsters from reaching the door
Kill 1000 enemies
Kill 10.000 enemies
Kill 50.000 enemies
Build 10 towers
Build 100 towers
Build 500 towers
Build 1000 towers
Win 1 game
Win 10 games
Win 30 games
Win 50 games
Force a 30 tile path for enemies
Force a 50 tile path for enemies
Force a 70 tile path for enemies
Force a 90 tile path for enemies
Killed the Shaman
Killed the Demon Prince
Killed the Skeleton King
Killed the Massive Slime
Killed the Necromancer
Killed the Undead Demon
Killed all the Titans