Here is the full list of all 33 Niffelheim achievements.
Complete 3 quests of the Priests
Craft 100 Alchemy items
Activate 5 Charms
Kill 10 Buffalos
Use 20 different Potions
Activate the Dragon
Eliminate 3 Bosses in underground caves
Kill 30 Spiders
Collect 10 Charms
Craft 100 items in the Forge
Cut down 100 Trees
Build all constructions of the highest level in a single Land
Kill 300 Skeletons
Grow 200 Vegetables
Cook 100 dishes in the Kitchen Workshop
Consume 10000 HP
Expose 10 Graves
Complete 10 Quests
Build a lvl 1 stone Castle, Walls and Towers
Build a lvl 1 clay Castle, Walls and Towers
Build a lvl 1 wooden Castle, Walls and Towers
Kill 10 Bears
Kill 1000 Skeletons
Inflict 25,000 damage with a long-range weapon
Kill 500 enemies with your Dragon
Trade for 10,000 Gold
Collect 100 Golden Ore
Upgrade all Workshops to 9 lvl.
Survive for 50 days
Survive for 100 days
Survive for 200 days
Reach Asgard at least once!
Reach Asgard in 100 days!