You can miss this achievement to “Ashen” very fast! Head southwest to Sindre’s View, northwest of Tower of Gnomon (Flokir Side Journey).
Follow the path into the gorge, you will see a staircase on the right side, go along it. Once you have reached the top of the stairs, go directly to the left to the window, help your companion to climb up and you will be pulled up by him.
Now follow the path to the very top, where the achievement will be unlocked. For a better understanding you will find the procedure below in the video.
Discover the secret of Contemplation.
An overview of all available achievements can be found here.