Here is the full list of all 20 Age of Empires: Castle Siege (UWP) achievements worth 1,000 gamerscore.
Successfully defended your castle 10 times
Destroyed 40 Walls in Multiplayer Battles
Looted 100,000 Wood
Advanced to the Second Age
Looted 30,000 Food
Won 20 Multiplayer Battles
Unlocked the Ladder Invaders from the Barracks
Won 100 Crowns in Multiplayer Battles
Win 3 battles in the Historical Campaign
Destroy 30 Emplacements in Multiplayer Battles
Unlock the Catapult from the Siege Workshop
Upgrade an Archer Tower to level 5
Loot 60,000 Stone
Destroy the Keep 100 times in Multiplayer Battles
Unlock any 6 heroes
Build a Stable
Unlock each civilization's unique troop
Advance to the Eighth Age
Win 2000 Crowns in Multiplayer Battles
Fully upgrade each civilization's unique troop