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