Here is the full list of all 14 Unearthing Colossal achievements.
Boost yourself high into the air
You have defeated guardian Kasta
You have defeated guardian Vermis
You have defeated guardian Spandau
You have defeated the King of Humanity
You have defeated the Bringer of Life.
You have defeated unchosen guardian Arachnae
Forge a level 1 weapon using collected souls
Forge a level 2 weapon using collected souls
Forge a level 3 weapon using collected souls
Forge a helm in the soul furnace
Forge armor in the soul furnace
Forge pauldrons in the soul furnace
Forge greaves in the soul furnace