Tā juànniàn nà duàn wúyōu wúlǜ de tóngnián shíguāng.
She thinks fondly of those carefree childhood days.
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Literary and emotional — usually about places, the past, or loved ones one feels deeply attached to. Compare with 怀念 (huáiniàn, to miss / reminisce) which is more neutral, and 思念 (sīniàn, to miss someone) which is specifically about people.