-대단했지. 나는 제주도에 갔었어.

It was great. I went to jeju do. --> It was great! I had a good time in Jeju Island.

=> Corrected : The sentence is corrected grammatically.

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-재미있는 방학을 보냈구나.

You had fun vacation. --> You had a nice vacation.

=> Another way: Your sentence is okay and this is another way of saying it.

-응, 너무 즐거운 방학을 보냈어.

Yes, I had fun vacation. --> Yes, I had a good vacation.

=> Another way: Your sentence is okay and this is another way of saying it.

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