One of the simplest ways to restore calm is to go outside into nature.
Listen to the sounds.
Feel the air on your skin.
Experience the sun, the wind, the rain, the snow.
Touch the bark of a tree.
Inhale the scent of a flower.
Observe the wildlife.
Even in the middle of a busy city, you can experience the elements and see the sky. You can usually see a tree and hear the birds too.
Tune into the rhythm of nature wherever you are and notice your mind and emotions begin to settle.