back in the day

used for talking about a time in the past, usually when you are remembering nice things about that time

曾几何时(尤用于追忆美好往事时)

Back in the day, we had an apartment with a swimming pool.

曾几何时我们还有过一套带游泳池的公寓。

Back in the day, I used to spend my summers exploring or playing with friends. Now I'm in the office every day.

曾几何时我常常在夏天和朋友们一起探险或玩耍。现在我每天都在办公室。