Episode 2x02 -- "Brave New World"
"I came back to this town to start a life with you. We can't forget to live it." ~ Stefan
After Caroline transitioning to a vampire, Stefan wanted to offer Elena comic relief and give her a taste of normal. He took her to the Ferris Wheel at the town event to make her happy. Once at the top, she finally started laughing, causing Stefan to say, "it's just so nice to see you laugh."