Death's Door

This achievement will require quite a bit of work after you complete the main storyline, requiring you to find 7 "Ancient Tablets of Knowledge," some of which require lengthy steps to unlock:
 

1. Pink Tablet - Pieced together by finding the three owls referenced in In Caw-Hoots (25G) 
2. Red Tablet -  Jefferson the squid, the key player in A Stroll with Jefferson (25G), will take you to this tablet while he's on your back after a little adventure across the game world
3. Blue Tablet - Behind a door unlocked by lighting the six torches found around The Old Watchtowers at night with your fire spell
4. Yellow Tablet - Found after defeating four waves of enemies in a chest near the entrance of the Overgrown Ruins
5. Green Tablet -  Behind the door in Pothead's secret garden, opened after finding and planting all 50 life seeds referenced in Reap what you sow (50G) 
6. Purple Tablet - You must aquire the shiny thing "Mysterious Locket" found behind a door only open at night above the arena you fought Betty in The Old Watchtowers area. Once acquired return to the Old Cemetery and head towards the area the Gravedigger was located to find a now open door. After a cutscene and fight, the tablet will be in the area.
7. Cyan Tablet - Found by guiding the pink souls found at night in the Old Cemetery to nearby statues

After finding all the tablets, return to the Camp of Free Crows where the door at the back will open - proceed through the area and after the cutscene the achievement will unlock.