Here is the full list of all 12 Gnomes Garden 3: The Thief of Castles achievements worth 1,000 gamerscore.
For activating an altar
For speeding up construction
For getting rid of a Gremlin
For speeding up workers
For restoring a plant
For constructing a building
Grow a lily pad
Stop time
Restore Stonehenge
Restore the signal fires
Defeat the evil warlock
Complete all levels with 3 stars