Here is the full list of all 10 Dear Esther: Landmark Edition achievements worth 1,000 gamerscore.
Trigger all directors' commentary
Walk 5000 steps
Finish Chapter 'The Beacon'
Trigger all voice over points
Uncover 4 urns
Finish Chapter 'The Caves'
Finish Chapter 'The Buoy'
Finish Chapter 'The Lighthouse'
Die from falling off a cliff once
Drown Once