The Messenger

You reach section Rivière Turquoise in second part of game after beating Dark Cave section (with MISSABLE achievement "I Swear It's My First Time").

All you need to do is cross 2 main rooms and in 3th, just after entrance to the shop you need to use 3 blue flowers (they are just lifts), after 3rd you hit another blue flowers which give you achievement.

This can be done in Rivière Turquoise which is accessible after making your way through the Dark Cave. Go down from the starting point and go left one screen. Launch yourself with the flower pod and you'll bounce on the two flowers above. Once you're on the other side, climb back up and do it again. If that isn't enough to unlock the achievement, get up top and slash the right side flower to make it face right towards the wall, then launch yourself at it again.