A serene person, place, or thing is calm and peaceful, like a clear blue sky. And serenity is a feeling of being relaxed, happy, and quiet.
Serene weather and serene days are clear, sunny, and beautiful. They make you want to spend a serene afternoon in the hammock, soaking up the serenity, which means you're doing nothing at all but feeling joyful and at rest.
On the TV show Firefly, Malcolm Reynolds captains a spaceship named Serenity. He bought the ship after surviving a war, and it serves as a safe, secluded home for himself and his beloved crew amid a hostile, dangerous universe. Serenity has no weapons, but it has a candlelit dining room table that seats the whole crew. It's the perfect home: safe, and serene.