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