I think the lesson might be fun if we all imagined that we went to England on a trip and experienced lots of unexpected things, but all came safely back to Japan.
ご質問ありがとうございます。
"I think the lesson might be fun"=「レッスンは面白くなると思います」
"if we all imagined that we went to England on a trip"=「皆がイギリス旅行に行ったと想像して」
"and experienced lots of unexpected things,"=「そして多くの想定外なことを経験して」
"but all came safely back to Japan."=「でも皆無事に日本に帰って来たというふうに。」
ご参考に。