Here is the full list of all 20 There Was A Caveman achievements.
Complete caves without dying.
Complete the caves
Slay 100 turtles.
Die 10 times.
I quickly forget..
Complete the forest
Complete the underwater area
Complete the afterlife
Complete the snow plains
Complete the guts
Die 100 times.
Die 250 times.
Die 500 times!
Complete forest without dying.
Complete underwater without dying.
Complete afterlife without dying.
Complete snow plains without dying.
Complete guts without dying!
Have 100 skulls.
You found your love!