Doodling in a sketchbook is very stress-relieving and calming. I recommend it to everyone :)
You don't need any artistic skills.
All you need is paper and a pen :)
Or a sketchbook and a fountain pen with purple ink, as in my case.
Crosshatching was used to build up the shadows. It's probably my favourite drawing technique. Works best with pen and ink. This is the cover image for one of my children's picture books.