Some Thesaurus words for "serenity" - calmness, composure, cool, patience, peace, peace of mind, placidity, quietness, quietude, stillness, tranquility.
The blue sky in this photo just gives me the greatest amount of tranquility. I don't know whether it is the bright white of the blossoms against the brilliance blue or if it makes me feel like a small part of the world. It gives you such awareness that you are just a single entity and that there is so much more to appreciate other than what you have. I hope you take the time to enjoy the stillness around you if even for a few seconds!