Complete the indicated task to unlock the achievement.

Achievement	How to unlock
Portal 1	Complete level 6.
Portal 10	Complete level 60.
Portal 2	Complete level 12.
Portal 3	Complete level 18.
Portal 4	Complete level 24.
Portal 5	Complete level 30.
Portal 6	Complete level 36.
Portal 7	Complete level 42.
Portal 8	Complete level 48.
Portal 9	Complete level 54.