Here is the full list of all 15 Sokocat - there are Islands achievements.
Complete level 1
Complete level 5
Complete level 10
Complete level 15
Complete level 20
Complete level 25
Complete level 30
Complete level 35
Complete level 40
Complete level 45
Complete level 50
Throw a box in the water
Use bridge
Use platform
Restart an island 10 times.