It may sound a little cliché, but it can really help you relax and calm down: simply listening to birdsong and forest sounds.
At least that's what a Study , which comes to the conclusion that listening to bird calls is more relaxing than a guided meditation! And that after only one minute, in which the participants had listened to the bird calls and the other sounds in the forest!
So the next time you're really stressed, just listen to a little "forest music". You can find lots of good videos about it on Youtube. Just type " Birds Chimes in Forest " or another search term and enjoy the relaxation!