There are 7 flowers alike the one in the achievement artwork, scattered over the game. Collecting them not only unlocks this, but it is also necessary to get the good ending.
They are in following puzzles:
#2 - in the basket on right side of the room.
#6 - when you get the Evasion achievement, do not exit, return to left
#7 - behind the dead whale
#14 - just before the Hanoi towers puzzle
#15 - in the village where you have to grow corn
#19 - left from the door guarded by spider
#20 - behind the organ, right side of the screen