The atmosphere made me feel like I was in high school again.
Looking around I felt like I was a high school student once again.
"The atmosphere made me feel like I was in high school again."
Atmosphere - Your surroundings, the location you are at. This surrounding reminds you of when you were in high school.
"Looking around I felt like I was a high school student once again."
Looking around - seeing the people around you, old friends, makes you feel like you are in high school once again.
Once again, something you have returned to that you'd left earlier.
The atmosphere made me feel like I was in high school again.
（高校時代に戻った気持ちになりました。）
Atmosphere - 様子、雰囲気。この雰囲気が、高校時代を思い出させる、ということです。
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Looking around I felt like I was a high school student once again.
（回りを見ると、高校時代に戻った気持ちになりました。）
Looking around - 自分の周りにいる人（旧友）を見ると、高校時代に戻った気持ちになるということです。
Once again - 一度離れたところに再び戻ることを表します。
There was so many young people at the library I felt like I was back at high school.
I felt like I was in high school again when I went to the library. There was so many students there.
Both of these answers are good ways of saying that you felt like a high school student again because there was so many young people at the library.
When you say 'I was back at' something it means that you are referring to a past experience, hence why you felt as if you were 'back at high school'.
2例とも、図書館に若い人がたくさんいて、高校生に戻ったような気になったと伝える言い方です。
「I was back at something」は、過去の経験を表します。その経験があったから、高校生に戻った気持ちになったわけです。
Being at the library with all those high school students made me feel nostalgic.
Being at the library was reminiscent of high school
Having a sense of nostalgia can make you feel like you are right back where you were years ago, or remind you of a memorable time in your life.
Saying that "being at the library was reminiscent of high school" explains that it made you feel like you were transported to that time period again. It can make you feel the same way you felt when you were a certain age or in a specific circumstance.
「feel nostalgic（懐かしいと思う）」は、何年も前に戻った気持ちになること、昔の思い出がよみがえることを表します。
"Being at the library was reminiscent of high school"
（図書館にいたら、高校時代を思い出しました）
- 高校時代に戻った気持ちになったことを表します。その年齢や場面で感じたのと同じ気持ちになることなどをいいます。
Being here at the library with all of these high schoolers made me feel like I was one of them.
This library has so many high school students that it makes me feel like one too.
I felt like I was in high school again after being around so many of them at the library.
Being here at the library with all of these high schoolers made me feel like I was one of them.
This library has so many high school students that it makes me feel like one too.
I felt like I was in high school again after being around so many of them at the library.
It's funny how being around so many students makes me feel like I was also a student.
The library had so many students there that it made me feel like one too.
Being at the library around so many high school students reminded me of what it felt like to be one.
Being here at the library with all of these high schoolers made me feel like I was one of them.（こうして高校生と一緒に図書館にいたら、自分もその頃に戻ったみたいな気分になりました）
This library has so many high school students that it makes me feel like one too.（この図書館には高校生がたくさんいるので、自分もその頃に戻った気持ちになります）
I felt like I was in high school again after being around so many of them at the library.（図書館でたくさんの高校生と一緒にいたら、私もその頃に戻ったみたいな気分になりました）
It's funny how being around so many students makes me feel like I was also a student.（不思議なもので、たくさんの学生と一緒にいると自分もその頃に戻った気分になります）
The library had so many students there that it made me feel like one too.（図書館には学生がたくさんにて、自分もその頃に戻ったような気分になりました）
Being at the library around so many high school students reminded me of what it felt like to be one.（図書館でたくさんの高校生と一緒にいたら、自分が高校生だった頃を思い出しました）
I was at the local library and there were many high schoolers there. It felt like I was in high school again.
When you want to explain that you were at the library and there were many high school students there, which made you feel like you were in high school again, you may express this in the following way:
-I was at the local library and there were many high schoolers there. It felt like I was in high school again.
「図書館に行ったら高校生がたくさんいて、高校時代に戻ったような気持ちになった」は、次のように表せます。
-I was at the local library and there were many high schoolers there. It felt like I was in high school again.
（地元の図書館に行ったら高校生がたくさんいて、高校時代に戻ったような気持ちになりました）
"I almost felt like I was back in school"
This expression is expressing that it almost/nearly felt/was like being in school again.
"The atmosphere was almost like high school again"
'Atmosphere' is an expression that refers to the feeling/mood/demeanor of a place.
"I almost felt like I was back in school"（学生時代に戻ったような気持ちになった）
この文は、「学生時代に戻ったような気持ちになった」と伝えています。
"The atmosphere was almost like high school again"（学生時代に戻ったような雰囲気だった）
'Atmosphere' は、場所の「雰囲気」や「ムード」を指します。
The atmosphere made me feel like i was a high schooler again
There were many young people in the library and i felt like a high schooler again
Someone that goes to high school is called a 'high schooler' young people refers to the age of the people usually in their teenage years
atmosphere is the mood or feelings of a place
こんにちは。
さまざまな言い方ができると思いますが、下記のような英語表現はいかがでしょうか：
It felt like I was in high school again.
また高校時代に戻ったみたいだった。
It felt like we were back in high school.
また高校生になったみたいだった。
feels like ... で「〜のように感じる」、felt like ... で「〜のように感じた」です。
ぜひ参考にしてください。
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