Here is the full list of all 15 Landnama achievements.
The base game contains 11 achievements, and there is 1 DLC pack containing 4 achievements.
Complete a settlement
Find a landmark
Complete a saga
Complete a settlement without manually pausing
Complete a settlement before the 7th winter
Survive one settlement for 25 winters
Explore a tile 15 tiles away from the homestead
Reach 25 production per harvest
Complete a saga in less than 40 winters
Find all landmarks in one saga
Complete a saga with all hagalaz runes enabled
Complete a settlement with a only one house
Explore all 25 unique tiles in one settlement
Reach 25 production from the Gothi
Complete a settlement without choosing masteries