My word brainstorming list for quiet:

• classical music
• nature - birds chirping
• soothing
• taking a bath
• stillness
• the sound of your footsteps (or own breath)
• crunching of leaves
• feeling small in a big, big world
• sun and blue skies
• concentration, focus
• no interruptions or distractions (thinking of tech here)
• relaxation
• yoga 
• declutter
• clouds passing by
• solitude, being by yourself
• personal enjoyment
• lost in thought

I narrowed down my concept sketches to nature scenes because that's when I can truly disconnect from my daily distractions and connect with Mother Nature, uninterrupted.

This sketch shows a girl standing/sitting still and looking out toward the rolling hills on a quiet, sleepy farm.  

This sketch is of someone standing in a forest, surrounded by old majestic 100+year old trees and new ones. The sun peeks through the canopy of the trees, creating random pockets of sunlight streaks.