Here is the full list of all 12 Lost Artifacts: Soulstone achievements worth 1,000 gamerscore.
For defeating the Villain
For completing all levels with 3 stars
For stopping time
For restoring monks’ altars
For destroying towers
For activating an altar
For speeding up construction
For restoring the water wheel
For speeding up archaeologists
For defeating the Evil Savage
For restoring a statue
For constructing a building